Particle beam isotope generator apparatus, system and method

ABSTRACT

An isotope generation apparatus is disclosed including: an ion beam source of any of the types described herein; an extractor for extracting the ion beam from the confinement region, where the beam includes a portion of multiply ionized ions in a selected final ionization state; a target including a target material; and an accelerator for accelerating the ion beam and directing the ion beam to the target. The ion beam directed to the target transmutes at least a portion of the target material to a radio-isotope in response to a nuclear reaction between ions in the selected final ion state and atoms of the target material.

CROSS REFERENCE TO RELATED APPLICATION

This application is related to and claims benefit of U.S. ProvisionalApplication 61/178,857 filed May 15, 2009, the contents of which areincorporated by reference in their entirety.

BACKGROUND

This disclosure is related to ion sources, and more particularly to highintensity ion sources.

Ion sources may be used to generate ion beams useful in a number ofapplications. For example, the beams may be used to bombard targets todrive nuclear reactions for the production of isotopes.

Some ions sources ionize neutral targets via collisions with energeticelectrons.

Electron Cyclotron Resonant (ECR) plasma sources generate energeticelectrons by exciting the cyclotron motion of the electrons within amagnetic field. The ECR plasma source is located in a vacuum chamber tocontrol the gas that is ionized, and to reduce the pressure allowing theelectrons to reach ionization energy.

A charged particle placed in a uniform magnetic field will gyrate aroundthe magnetic field with a frequency given by the electron cyclotronfrequency.

$\omega_{ce} = \frac{eB}{m}$

If the magnetic field is not uniform, the electron still gyrates aroundthe magnetic field, but the orbit and frequency become somewhat morecomplicated. ECR ion sources do not require a uniform magnetic field tooperate. In fact, many of them operate in highly non-uniform magneticfields. By applying an oscillating electric field, the cyclotron motionof the electrons can be excited. If the oscillating electric field isresonant with the electron cyclotron frequency and couples to theelectron motion, the electrons will gain energy. The highest couplingwould be an electric field that rotated about the magnetic field in thesame direction as the electrons, and at the same rate. This electricfield would look like a DC electric field in the frame of the electrons.Good coupling can also be obtained with a linear polarized electricfield that oscillates perpendicular to the magnetic field. As theelectrons gain energy they will collide with any gas within the source,ionizing the background gas. This forms plasma and creates moreelectrons that can ionize more background gas. This prior art processcontinues as the plasma density increases until losses are balanced withproduction.

In prior art devices, the balance occurs long before a powerful beam canbe generated, and a powerful beam is what is needed to strike andtransmute target material into such things as useful medical isotopes.Many isotopes are, in theory, thought to be useful, but heretofore theirsmall obtainable quantities and short half lives, prevent their use.

SUMMARY

The inventors have realized that a high intensity source of multiplycharged ions in a selected ionization state may be provided. Forexample, some embodiments of the devices, systems and techniquesdescribed herein produce a high density beam of ions, useful inproducing long and/or short half-live isotopes or for use directly (e.g.for the treatment of tumors). Some embodiments produce a beam ofmultiply ionized particles in selected final ionization state. Someembodiments produce a high density beam of ions that are highly ionized.Some embodiments produce a beam of multiply ionized He relativelyeconomically.

Some embodiments use ion beams to transmute atoms and isotopes intouseful isotopes that can not be produced in quantity by other means.Some embodiments enable production of isotopes, heretofore not availablein useful quantities.

Some embodiments use ion beams to transmute isotopes, such as thoseproduced in commercial nuclear power plants, into fuel that can berecycled into the reactor. Some embodiments provide a machine which canbe sited adjacent a commercial nuclear power plant to transmute longhalf life isotopes, such as those produced in commercial nuclear powerplants, into short half life isotopes which quickly decay into stableatoms without the requirement of transportation or burial.

In one aspect, an ion source is disclosed including: a chamber disposedabout a longitudinal axis and containing a gas. The source includes amagnetic confinement system configured to produce a magnetic field in aconfinement region within the chamber, where the confinement region isdisposed about the axis and extends along the axis from a proximal endto a distal end. The magnetic field includes: a first magnetic mirrorlocated at the proximal end of the confinement region; a second magneticmirror located at the distal end of the confinement region; and asubstantially uniform magnetic field disposed about and directedsubstantially parallel to the longitudinal axis, the substantiallyuniform magnetic field being located between the first and secondmagnetic mirrors. The system also includes an electron cyclotronresonance driver which produces a time varying electric field whichdrives the cyclotron motion of electrons located within the confinementregion, the driven electrons interacting with the gas to form a confinedplasma. During operation, the magnetic confinement system confines theplasma in the confinement region such that a portion of atoms in theplasma experience multiple ionizing interactions with the drivenelectrons to form multiply ionized ions having a selected finalionization state.

In some embodiments, the first and second magnetic mirrors each includea non-uniform magnetic field, where the field: is directed substantiallyalong the longitudinal axis, and has a magnitude which increases as afunction of axial distance from the substantially uniform magnetic fieldto a peak magnitude greater than the magnitude of the substantiallyuniform magnetic field. In some such embodiments, the peak magnitude ofthe first magnetic mirror is greater than the peak magnitude of thesecond magnetic mirror. In some embodiments, the peak magnitude of themirrors may be equal or substantially equal. In some embodiments, thepeak magnitude of each of the first and second magnetic mirrors isgreater than about twice the magnitude of the substantially uniformmagnetic field. In some embodiments the peak magnitude of each of thefirst and second magnetic mirrors may take any other suitable values,e.g., one and a half, three, four, five, or more times the magnitude ofthe substantially uniform magnetic field.

In some embodiments, the magnitude of the substantially uniform magneticfield is a local axial minimum of the magnetic field in the confinementregion.

Some embodiments include an extractor for extracting a beam of ions fromthe confinement region, where the beam includes a portion of themultiply ionized ions in the selected final ionization state.

In some embodiments, the ion beam has a current of 1 mA or greater, 10mA or greater, 20 mA or greater, or even 50 mA or greater.

In some embodiments, at least 50% of the ions in the beam (as measuredby particle fraction, or as a percentage of total beam current) are inthe selected final ionization state. In some embodiments, at least 60%,70%, 80%, or 90% of the ions in the beam are in the selected finalionization state.

In some embodiments, the electron cyclotron resonance driver produces atime varying electric field having a frequency substantially tuned tothe electron cyclotron resonance frequency corresponding to thesubstantially uniform magnetic field

In some embodiments, the electron cyclotron resonance driver drives thecyclotron motion of electrons located throughout a volume containing thesubstantially uniform magnetic field.

In some embodiments, the magnitude of the substantially uniform magneticfield varies by less than 1%, less than 5%, or less than 10% over aregion disposed about the longitudinal axis, the region located between(e.g. midway between) the first and second magnetic mirrors andextending along the longitudinal axis over a distance equal to at leastabout 10%, 15%, 25%, or even more of the axial distance between thefirst and second magnetic mirrors.

In some embodiments, the magnitude of the substantially uniform magneticfield varies by less than 1%, less than 5%, or less than 10% over aregion extending at least 5 cm, 10 cm, 15 cm, or greater along thelongitudinal axis.

In some embodiments, the magnetic field is azimuthally symmetric aboutthe longitudinal axis throughout the confinement region.

In some embodiments, the electron cyclotron de-correlation time forelectrons driven by the electron cyclotron resonance driver is at leaston the order of an average confinement time for a heated electron in theconfinement region.

In some embodiments, the electron cyclotron resonance driver drives atleast a portion of the electrons in the volume to an energy of about 200eV or more, about 300 eV or more, or about 1 keV or more.

Some embodiments include an ion cyclotron driver, which directsradiation to the confinement region to preferentially drive thecyclotron motion of ions in the plasma having a selected drivenionization state to increase the motional energy of the ions indirections perpendicular to the longitudinal axis. In some embodiments,the ion cyclotron driver preferentially increases the confinement timein the confinement region of the ions having selected driven ionizationstate, thereby increasing the number of the ions undergoing furtherionizing interactions with the electrons in the containment region toform ions having the selected final ionization state. In someembodiments, the ion cyclotron driver directs radiation to theconfinement region having a frequency substantially tuned to the ioncyclotron frequency of the ions having the selected driven ionizationstate in the substantially uniform magnetic field. In some embodiments,the selected driven ionization state is a singly ionized state. In someembodiments, the selected driven ionization state is a multiply ionizedstate having an ionization state less than the final ionization state.

In some embodiments, the ion cyclotron driver directs radiation to theconfinement region at a plurality of frequencies each substantiallytuned to the ion cyclotron frequency of ions having a respectiveselected driven ionization state in the substantially uniform magneticfield,

In some embodiments, the ion cyclotron driver includes an antenna suchas a filar antenna (e.g. a single or bi-filar), a capacitor plate, anuntwisted bi-filar antenna or an untwisted filar antenna, orcombinations thereof.

In some embodiments, at least one magnetic mirror includes a magneticfield extending outside of the confinement region. The electroncyclotron driver is tuned to the electron cyclotron frequencycorresponding to a portion of the magnetic field extending outside ofthe confinement region to drive the cyclotron motion of unconfinedelectrons in the portion of the field, where the unconfined electronsinteract with the gas to form an unconfined plasma. The ion sourcefurther includes a sputter target located in the chamber and proximal tothe portion of the magnetic field, and biased to attract ions from theunconfined plasma. In response to collisions with the attracted ions,the sputter source emits neutral particles which form at least a portionof the gas of atoms. In some embodiments, at least a portion of theemitted neutral particles interact with the unconfined electrons to formions which are attracted back to the sputter source.

In some embodiments, the sputter target includes an annulus of materialdisposed about the longitudinal axis, an annulus of material disposedabout the longitudinal axis and having a target surface which is angledwith respect to the longitudinal axis, or target material positionedabout and extending along the longitudinal axis, or combinationsthereof.

In some embodiments, the gas includes He atoms, and the magneticconfinement system confines the plasma in the confinement region suchthat a portion of He atoms in the plasma experience two singly ionizinginteractions with the driven electrons to form alpha particles or ³He⁺⁺ions. Some such embodiments include an extractor for extracting abeam ofHe ions from the confinement region, where the beam includes alphaparticles and/or ³He⁺⁺ ions.

In some embodiments, the beam of He ions has a current of 1 mA orgreater, 10 mA, or 20 mA or greater. In some embodiments, at least 50%,at least 70%, at least 80%, or at least 90 or more of the ions in thebeam are alpha particles and/or ³He⁺⁺ ions.

In some embodiments, the magnetic confinement system is furtherconfigured to produce a radial confinement magnetic field which confinesthe radial motion of the plasma away from the longitudinal axis. Theradial confinement magnetic field does not substantially extend into thesubstantially uniform magnetic field. In some embodiments, magneticconfinement system includes a multipole radial confinement magnetdisposed about the longitudinal axis which produces a magnetic fielddirected azimuthally to the longitudinal axis and having a magnitudewhich decreases radially with increasing proximity to the axis, exceptalong one or more cusps. In some embodiments, the multipole magnetincludes 8 or more poles.

In some embodiments, the electron cyclotron resonance driver produces atime varying electric field having a frequency substantially de-tuned tothe electron cyclotron resonance frequency corresponding to thesubstantially uniform magnetic field. In some embodiments, the electroncyclotron resonance driver drives the cyclotron motion of electronslocated in a first region of non-uniform magnetic field distal thesubstantially uniform magnetic field along the longitudinal axis and asecond region of non-uniform magnetic field proximal the substantiallyuniform magnetic field along the longitudinal axis. In some embodiments,each of the first and second regions of non-uniform magnetic fieldinclude a surface of points characterized such that the frequency of thetime varying electric field is tuned to the electron cyclotron resonancefrequency of the non-uniform magnetic field at the points.

In some embodiments, the substantially uniform magnetic field has amagnitude of about 0.1 T or greater, 0.5 T or greater, or 6 T orgreater.

In some embodiments, the gas includes molecules, and the drivenelectrons interact with the gas to disassociate the molecules to formthe confined plasma.

In another aspect, a method of generating an ion beam is disclosed,including: providing a chamber disposed about a longitudinal axis andcontaining a gas and producing a magnetic field in a confinement regionwithin the chamber, where the confinement region is disposed about theaxis and extends along the axis from a proximal end to a distal end. Themagnetic field includes: a first magnetic mirror located at the proximalend of the confinement region; a second magnetic mirror located at thedistal end of the confinement region; a substantially uniform magneticfield disposed about and directed substantially parallel to thelongitudinal axis, the substantially uniform magnetic field beinglocated between the first and second magnetic mirrors. The methodfurther includes producing a time varying electric field to drive thecyclotron motion of electrons located within the confinement region;causing the driven electrons interacting with the gas to form a confinedplasma; and confining the plasma in the confinement region such that aportion of atoms in the plasma experience multiple ionizing interactionswith the driven electrons to form multiply ionized ions having aselected final ionization state.

In some embodiments, the first and second magnetic mirrors each includea non-uniform magnetic field, where the field is directed substantiallyalong the longitudinal axis and has a magnitude which increases as afunction of axial distance from the substantially uniform magnetic fieldto a peak magnitude greater than the magnitude of the substantiallyuniform magnetic field, In some embodiments, the peak magnitude of thefirst magnetic mirror is greater than the peak magnitude of the secondmagnetic mirror (in other embodiments they may be equal or substantiallyequal).

In some embodiments, a peak magnitude of each of the first and secondmagnetic mirrors is greater than about twice (or 1.5, 3, 4, 5, etctimes) the magnitude of the substantially uniform magnetic field.

In some embodiments, the magnitude of the substantially uniform magneticfield is a local axial minimum of the magnetic field in the confinementregion.

Some embodiments further include extracting the ion beam from theconfinement region, where the beam includes a portion of the ions whichare in the selected final ionization state. In some embodiments, the ionbeam has a current of 1 mA or greater, 10 mA or greater, 20 mA orgreater, or 50 mA or greater.

In some embodiments, at least 50%, 60%, 70%, 80% or 90% or more of theions are in the selected final ionization state.

In some embodiments, the time varying electric field has a frequencysubstantially tuned to the electron cyclotron resonance frequencycorresponding to the substantially uniform magnetic field. In someembodiments, the electron cyclotron resonance driver drives thecyclotron motion of electrons located throughout a volume surroundingthe substantially uniform magnetic field.

In some embodiments, the magnitude of the substantially uniform magneticfield varies by less than 1%, 5%, 10%, or 15% over a region disposedabout the longitudinal axis, the region located midway between the firstand second magnetic mirrors and extending along the longitudinal axisover a distance equal to at least about 5%, 10%, 25%, 50%, or more ofthe axial distance between the first and second magnetic mirrors.

In some embodiments, the magnitude of the substantially uniform magneticfield varies by less than 1%, 2.5%, 5%, or 10% over a region extendingat least 1 cm, 2 cm, 5 cm, 10 cm, 15 cm, or 25 cm or more along thelongitudinal axis.

In some embodiments, the magnetic field is azimuthally symmetric aboutthe longitudinal axis throughout the confinement region.

In some embodiments, the electron cyclotron de-correlation time for thedriven electrons is at least on the order of an average confinement timefor a heated electron in the confinement region.

Some embodiments include driving the cyclotron motion of electronslocated within the confinement region to produce an electron energy ofabout 200 eV or more, 300 eV or more, or 1 keV or more.

Some embodiments further include directing radiation to the confinementregion to preferentially drive the cyclotron motion of ions in theplasma having a selected driven ionization state to increase themotional energy of the ions in directions perpendicular to thelongitudinal axis. In some embodiments, directing radiation to theconfinement region to preferentially drive the cyclotron motion of ionsin the plasma having a selected driven ionization state includespreferentially increasing the confinement time in the confinement regionof the ions having selected driven ionization state, thereby increasingthe number of the atoms undergoing further ionizing interactions withthe electrons in the containment region. In some embodiments, directingradiation to the confinement region to preferentially drive thecyclotron motion of ions in the plasma having a selected drivenionization state includes: directing radiation to the confinement regionhaving a frequency substantially tuned to the ion cyclotron frequency ofthe ions having the selected driven ionization state in thesubstantially uniform magnetic field. In some embodiments, the selecteddriven ionization state is a singly ionized state. In some embodiments,the selected driven ionization state is a multiply ionized state havingan ionization state less than the final ionization state. Someembodiments include directing radiation to the confinement region at aplurality of frequencies, each frequency substantially tuned to the ioncyclotron, frequency of ions having a respective selected drivenionization state in the substantially uniform magnetic field,

In some embodiments, directing radiation to the confinement region topreferentially drive the cyclotron motion of ions in the plasma having aselected driven ionization state includes: directing radiation from anantenna of the types disclosed herein.

In some embodiments, at least one magnetic mirror includes a magneticfield extending outside of the confinement region. The frequency of thetime varying electric field is tuned to the electron cyclotron frequencycorresponding to a portion of the magnetic field extending outside ofthe confinement region to drive the cyclotron motion of unconfinedelectrons in the portion of the field, where the unconfined electronsinteract with the gas to form an unconfined plasma. The method mayfurther include providing a sputter target located in the chamber andproximal to the portion of the magnetic field and biasing the sputtertarget to attract ions from the unconfined plasma, such that, inresponse to collisions with the attracted ions, the sputter source emitsneutral particles which form at least a portion of the gas of atoms. Insome embodiments, at least a portion of the emitted neutral particlesinteract with the unconfined electrons to form ions which are attractedback to the biased sputter source. In some embodiments, the sputtertarget includes an annulus of material disposed about the longitudinalaxis; an annulus of material disposed about the longitudinal axis andhaving a target surface which is angled with respect to the longitudinalaxis, or a target material positioned about and extending along thelongitudinal axis, or combinations thereof.

In some embodiments, the gas includes He atoms, and the method includesconfining the plasma in the confinement region such that a portion ofthe He atoms in the plasma experience two singly ionizing interactionswith the driven electrons to form alpha particles or ³He⁺⁺.

Some embodiments include extracting a beam of He ions from theconfinement region, where the beam includes alpha particles or ³He⁺⁺ions. In some embodiments, the beam of He atoms has a current of 1 mA orgreater, or 20 mA or greater. In some embodiments, at least 50%, 60%,70%, 80%, or 90% or more of the ions in the beam are alpha particles. Insome embodiments at least 50%, 60%, 70%, 80%, or 90% or more of the ionsin the beam are or ³He⁺⁺.

Some embodiments further include producing a radial confinement magneticfield which confines the plasma radially. The radial confinementmagnetic field does not substantially extend into the substantiallyuniform magnetic field. In some embodiments, producing a radialconfinement magnetic field includes producing a magnetic field directedazimuthally to the longitudinal axis and having a magnitude whichdecreases radially with increasing proximity to the axis, except alongone or more cusps.

Some embodiments include producing a time varying electric field havinga frequency substantially de-tuned to the electron cyclotron resonancefrequency corresponding to the substantially uniform magnetic field.Some embodiments include driving the cyclotron motion of electronslocated in a first region of non-uniform magnetic field distal thesubstantially uniform magnetic field along the longitudinal axis and asecond region of non-uniform magnetic field proximal the substantiallyuniform magnetic field along the longitudinal axis. In some embodiments,each of the first and second regions of non-uniform magnetic fieldinclude a surface of points at which the frequency of the time varyingelectric field is tuned to the electron cyclotron resonance frequency ofthe non-uniform magnetic field at the points. Some such embodimentsinclude effecting stochastic heating of electrons in the confinementregion which pass through the first and second regions multiple times.

In some embodiments, the substantially uniform magnetic field has amagnitude of about 0.1 T or greater, 0.5 T or greater or 0.6 T orgreater.

In some embodiments, the gas includes molecules, and the causing thedriven electrons interacting with the gas to form a confined plasmaincludes disassociating the molecules.

In another aspect, a method is disclosed including: generating an ionbeam using any of the devices and techniques described herein, directingthe ion beam to a target including a target material; and transmuting atleast a portion of the target material to a radio-isotope by a nuclearreaction between ions in the selected final ion state and atoms of thetarget material.

In some embodiments, the atoms of the target material have a longer halflife than the radio-isotope.

In some embodiments, the ions in the selected final ion state includealpha particles or ³He⁺⁺ ions.

In some embodiments, the nuclear reaction between ions in the selectedfinal ion state and atoms of the target material include at least onefrom the list consisting of: ⁹⁶Zr(α,n)⁹⁹Mo, ²⁰⁹Bi(α,2n)²¹¹At,¹⁴⁴Sm(α,γ)¹⁴⁸Gd, ¹¹⁶Cd(α,3n)^(117m)Sn and ¹¹⁴Cd(α,n)^(117m)Sn and¹⁴⁷Sm(α,3n)¹⁴⁸Gd.

In some embodiments, where the radio-isotope includes ⁹⁹Mo, and themethod further includes: generating a diagnostic or therapeuticeffective dose of ^(99m)Tc from the ⁹⁹Mo by negative beta decay. In someembodiments, the entire diagnostic or therapeutic effective dose of 99mTc is generated without the use of a nuclear fission reactor.

In some embodiments, the radio-isotope includes ¹¹¹In, and the methodfurther includes: generating a diagnostic or therapeutic effective doseof ¹¹¹In. In some embodiments, the entire diagnostic or therapeuticeffective dose of ¹¹¹In is generated without the use of a nuclearfission reactor.

In some embodiments, the radio-isotope includes at least one selectedfrom the list consisting of: ¹⁸F, ₁₂₃Xe, ¹²³I, ⁶⁷Ga, ¹¹¹In, ¹³¹Ba, ⁶⁸Ge,⁸²Sr, ⁸²Rb, ⁸⁹Sr, ¹⁵³Sm, ¹²⁴I, ²¹¹At, ¹⁴⁸Gd, ⁷⁶Br, ¹⁹⁹Tl, ¹⁰⁰Pd, ¹²⁸Ba,^(117m)Sn, and ²²⁹Th.

In some embodiments, the nuclear reaction includes fission of atoms inthe target material stimulated by bombardment with the ions in theselected final state.

In some embodiments, the target includes a layer of a first targetmaterial overlaying a second target material, The method furtherincludes: directing the ion beam at a first energy to the layer of firsttarget material such that a first portion of the ions in the beamtransmute a portion of the first target material into a firstradio-isotope by a first nuclear reaction between the first portion ofions and atoms of the first target material; a second portion of theions in the beam interact with the layer to be decelerated to a secondenergy, and the second portion of the ions in the beam transmute aportion of the second target material into a second radio-isotope by asecond nuclear reaction between the second portion of ions and atoms ofthe second target material. In some embodiments, the ions at the firstenergy more preferentially drive the first nuclear reaction than thesecond nuclear reaction, and the ions at the second energy morepreferentially drive the second nuclear reaction than the first nuclearreaction. In some embodiments, the first target material includes ¹⁰⁹Ag,the second target material includes ⁹⁶Zr, the first nuclear reactionincludes ¹⁰⁹Ag(α,2n)¹¹¹In, the second nuclear reaction includes⁹⁶Zr(α,n)⁹⁹Mo, the first energy is about 28 MeV, and the second energyis about 16 MeV.

In another aspect, an isotope generation apparatus is disclosedincluding: an ion beam source of any of the types described herein; anextractor for extracting the ion beam from the confinement region, wherethe beam includes a portion of multiply ionized ions in a selected finalionization state; a target including a target material; and anaccelerator for accelerating the ion beam and directing the ion beam tothe target. The ion beam directed to the target transmutes at least aportion of the target material to a radio-isotope in response to anuclear reaction between ions in the selected final ion state and atomsof the target material.

In some embodiments, the atoms of the target material have a longer halflife than the radio-isotope.

In some embodiments, the ions in the selected final ion state includealpha particles or ³He⁺⁺ ions.

In some embodiments, the nuclear reaction between ions in the selectedfinal ion state and atoms of the target material include ⁹⁶Zr(α,n)⁹⁹Mo,²⁰⁹Bi(α,2n)²¹¹At, ¹⁴⁴Sm(α,γ)¹⁴⁸Gd, and/or ¹⁴⁷Sm(α,3n)¹⁴⁸Gd.

In some embodiments, the radio-isotope includes ¹⁸F, ¹²³Xe, ¹²³I, ⁶⁷Ga,¹¹¹In, ¹³¹Ba, ⁶⁸Ge, ⁸²Sr, ⁸²Rb, ⁸⁹Sr, ¹⁵³Sm, ¹²⁴I, ²¹¹At, ¹⁴⁸Gd, ⁷⁶Br,¹⁹⁹Tl, ¹⁰⁰Pd, ¹²⁸Ba, and/or ²²⁹Th.

In some embodiments, the target includes a layer of a first targetmaterial overlaying a second target material.

In some embodiments, the accelerator directs the ion beam at a firstenergy to the layer of first target material such that: a first portionof the ions in the beam transmute a portion of the first target materialinto a first radio-isotope by a first nuclear reaction between the firstportion of ions and atoms of the first target material; a second portionof the ions in the beam interact with the layer to be decelerated to asecond energy, and the second portion of the ions in the beam transmutea portion of the second target material into a second radio-isotope by asecond nuclear reaction between the second portion of ions and atoms ofthe second target material. The ions at the first energy morepreferentially drive the first nuclear reaction than the second nuclearreaction, and the ions at the second energy more preferentially drivethe second nuclear reaction than the first nuclear reaction.

Various embodiments may include any of the above described featureseither alone or in any combination.

It is to be understood that as used herein, the term gas may refer to asingle component gas (e.g. ⁴He gas), or a multi-component gas (e.g.³He/⁴He gas mix, a He/Xe gas mix, a He/O₂ gas mix, etc.).

Scientific notation known in the art has been used herein to describevarious nuclear reactions. For a reaction described in the form A(b,c)D,“A” is the target nucleus, or irradiated material, “b” is a bombardingparticle, “c” is an, emitted particle, and “D” is the product orresidual nucleus. For a reaction described in the form A(b,c)D1(D2), D1and D2 primary and secondary products of the reaction.

These and other aspects of the present invention will become apparent tothose skilled in the art after considering the following detailedspecification along with the accompanying drawings where:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an ion beam system;

FIG. 1A is a block diagram of an ion beam system for making usefulisotopes;

FIG. 1B is a block diagram of an ion beam system adapted for treatmentof radio active waste from commercial nuclear power plants;

FIG. 1C is a block diagram of an ion beam system adapted for medicaltreatment, e.g. treatment of internal growths;

FIG. 2A is an operational schematic of an ion beam system

FIG. 2B is an operational schematic of an ion beam system showingmodified insulators;

FIG. 2C is an operational schematic of an ion beam system showing agrounded chamber;

FIG. 2D is an operational schematic of an ion beam system showingexternal ICR antenna.

FIG. 3A is a graph of the cross-section for formation of He⁺ and He⁺⁺electron impact on neutral He versus electron energy;

FIG. 3B is a graph of electron impact ionization cross-section for thefirst six ionization states of Xenon;

FIGS. 3C and 3D shows graphs of the cross-sections for electron impactionization as a function of electron energy, of neutral He(He+e⁻→He⁺2e⁻) and He⁺ (He⁺+e⁻→He⁺⁺2e⁻);

FIG. 4 is a graph of magnetic field magnitude as a function of axialposition in an ion source;

FIG. 5 is a graphical view of the loss cone associated with the magneticfields of FIG. 4;

FIGS. 6A and 6B are schematic diagrams of capacitor plate ICR antennae,FIG. 6A depicting a linear drive system and FIG. 6B depicting a circulardrive system with the horizontal plates driven 90° out of phase with thevertical plates.

FIG. 7 is a schematic diagram of a split ring antenna system for theICR;

FIG. 8 is schematic diagram of a bi-filer antenna where the to coils aredriven 90° out of phase to generate a rotating electric field for theICR;

FIG. 9 is schematic diagram of an untwisted bi-filer antenna where thetwo coils are driven 90° out of phase to generate a rotating electricfield for the ICR;

FIGS. 10A and 10B are graphical representations of the ECR resonancezones for the magnetic confinement fields when the ECR is operating inan on-resonant and an off-resonant mode, respectively;

FIG. 11 is a simplified cross-sectional view of a sputter sourceimplemented with an axially located target, showing different supportand bias material, and sputter material;

FIG. 12 is a simplified cross-sectional view of a sputter sourceimplemented with an annular target;

FIG. 13 is a simplified cross-sectional view of a sputter sourceimplemented as a conical sputter target;

FIG. 14 shows a multipole radial confinement magnet.

FIG. 14A shows the magnetic field generated by a multipole radialconfinement magnet.

FIG. 15 is a plot of total extracted beam current as a function ofcentral magnetic field strength for an ion beam system.

FIG. 16 shows time-of-flight mass spectrometer data for an ion beamgenerated in the ECR resonant mode of operation.

FIGS. 17A-C illustrate an exemplary target and target feed system.

DETAILED DESCRIPTION

Referring to FIG. 1, an Ion beam generator 11 generates an ion beam anddirects it to target 12 to cause a nuclear reaction, e.g. to transmuteatoms in target 12 to produce a desired isotope. Ion beam generator 11includes an ion source 10 of the type described herein, which produces abeam (e.g. a high intensity beam) including ions in a selected finalionization state. Ion beam generator 11 also includes a beam accelerator13, which accelerates the beam from source 10, and directs it to target12. Optionally, ion beam generator 11 also includes a filter forfiltering ions ion the beam, e.g. based on the charge or mass of theions. In some embodiments, accelerator 13 acts as a filter. For example,a cyclotron accelerator will naturally separate ions having differentionization states.

Beam accelerator 13 may be any suitable accelerator known in the art. Insome embodiments, the accelerator system is a hybrid RFQ-DTL (RadioFrequency Quadrapole-Drift Tube LINAC) system available for modificationfrom various vendors. Other accelerator systems such as almost any LINACor cyclotron could be used.

A number of coupling methods can be used between ion source 10 andaccelerator 13. For high intensity beams, a magnetic lens system isadvantageous. For low intensity beams, an electrostatic lens system ismore economic, compact, and effective. Generally, using a magnetic lensallows for an easy way to implement a particle filter that will rejectany He⁺ within the beam where the selected final ion state is He⁺⁺.

FIG. 1A shows a system 20 featuring ion beam generator 11. Ion beamgenerator 11 bombards target 12 with ions to transmute atoms in target12 to produce a desired isotope. The transmuted target undergoeschemical separation 15 to provide a pure sample of product isotope 16.In some embodiments, product isotope 16 is an intermediate product, andundergoes decay 17 resulting in final product 18. In some embodiments,the intermediate product is a relatively long lived radio-isotope incomparison to the final product isotope. In some embodiments, finalproduct 18 is an isotope suitable for use in medical treatment ordiagnostic applications, research applications (e.g. radio-marking),energy generation applications (e.g. as nuclear fuel), etc.

FIG. 1B shows a system 21 for treatment of nuclear waste 500. Nuclearwaste (e.g. commercial nuclear waste from power generation, research, ormedical use) undergoes chemical separation 501. Some long half lifewaste 502 not suitable for treatment is transferred to long termstorage. Other waste is included in target 12, which is bombarded withions from ion beam generator 11. In some embodiments, waste in target 12is transmuted into a relatively short half life product 504 whichundergoes decay 505 to become a stable product 506, which may be easilydisposed of. In some embodiments, waste in target 12 is transmuted tousable fuel 507, and is thereby recycled.

FIG. 1C shows a system for medical treatment. Ion beam generator 11generates an ion beam which is directed by probe 600 to human or animalbody 601 in order to treat tissue in the body. For example, in someembodiments, the ion beam is directed to a tumor 602 in body 601. Someembodiments include producing accelerated particles useful in treatinginterior tumors and the like wherein the particles (such as H⁺, He⁺⁺,C⁺⁴, C⁺⁶, or O⁺⁸) loose energy very slowly until at a certain energystate, substantially all of the particle's energy is transferred to thetumor.

FIGS. 2A, 2B, 2C, and 2D are operational diagrams of ion producingsystems using Helium (He) ions as an example. In order to understand theoperation of the devices described herein, it is helpful to understandthe issues in generating multiple charged ions. Although the ionizationof helium is discussed, the basic conclusions apply to all atoms, evenincluding hydrogen (H) and deuterium (²H) where a single electron isstriped from the atom to produce a proton (p) or deuteron (d),respectively.

If an ion source uses electron impact to ionize neutral atoms, the ratioof charge states formed can be determined by the cross sectionsinvolved. In the case of helium, the cross section for production ofHe⁺⁺ is more than two orders of magnitude below the cross section forthe production of He⁺ (see FIG. 3A). In general, prior art ionizationprocesses produce around 1% He⁺⁺ and 99% He⁺.

Changing the electron impact energy does not make a significant changein the production of He⁺⁺. The best overall performance is obtained nearthe peak of the He⁺⁺ cross section, approximately 300 eV. Usingsaturation of states and some other known tricks, it is possible togenerate a few percent He⁺⁺ with prior art devices.

For generating highly ionized states of any other atom, the problem ismade more difficult, by introducing more charge states, a greatervariation in the cross sections, and more dependence of the crosssections on the electron energy. This can be seen in FIG. 3B, where theelectron impact ionization for the first seven states of xenon (Xe) areshown.

It is difficult to obtain He⁺⁺ with a single electron collision. If morethen one electron collision is used, the fraction of He⁺⁺ can beincreased greatly because the cross section for production of He⁺⁺ fromHe⁺ is significantly higher than for the direct production of He⁺⁺ fromneutral He (see FIGS. 3C and 3D).

Table I summarizes the different reactions for helium.

TABLE I He + e⁻ → He⁺ + 2e⁻  0.35 × 10⁻¹⁶ 120 He⁺ + e⁻ → He⁺⁺ + 2e⁻0.045 × 10⁻¹⁶ 200 He + e⁻ → He⁺⁺ + 3^(e−) 0.001 × 10⁻¹⁶ 300

In order to ionize atoms by multiple collisions to reach a selectedfinal ionization state, it is necessary to confine the intermediatestates long enough for them to undergo additional electron collisions.In the case of helium, where He⁺⁺ is the selected final ionizationstate, it is necessary to confine the He⁺ long enough for it to undergoa second ionizing collision to form He⁺⁺. In the case of other atoms, itis necessary to retain the ion long enough for it to undergo severalionizing collisions to reach the selected state of ionization.

The systems described herein use a confining magnetic field to retainthe ions for the time required to reach the selected ionization state.In some embodiments, an azimuthally symmetric axial minimum magneticfield configuration is used. In other embodiments, a “true” minimummagnetic field configuration is used. For production of many ion chargestates (e.g. He⁺⁺) the simpler axial minimum field configuration seemsto be adequate. For production of highly charged states of some atoms, a“true” minimum magnetic field may be necessary.

FIG. 2A shows an exemplary ion source 10. Ionization chamber 30 isarranged along longitudinal axis A. Within the ionization chamber 30, alocal axial minimum magnetic field is formed between two magnetic mirrorfields 32 and 34 (field lines indicated with dashed lines), preferablygenerated by superconducting magnets 36 and 38. The local axial minimumfield is formed as central region of lower, substantially uniformmagnetic field 40, (field lines indicated with dashed lines). FIG. 4shows a plot of the magnitude of the fields 32, 34, and 40 as a functionof position along axis A for an exemplary field configuration.

As will be described in detail below, uniform field region 40 providesseveral beneficial effects which allow for the efficient production ofintense ion beams of ions in a selected, multiply ionized state. Inembodiments featuring axial minimum configurations, mirror fields 32, 34and central field 40 may each be azimuthally symmetric about axis A.

Referring back to FIG. 2A, although superconducting magnets are used insome embodiments, they are not required for production of the mirrorfields 32 and 34 in every instance. In some embodiments, the coils ofsuperconducting magnets are easier to adjust as the diameter of the wirecan be smaller, leaving more room for field adjustment. Refrigerationsystems, not shown, for superconducting magnets are commerciallyavailable.

The central magnetic field 40 can be implemented using a central magnet42, which may include copper coils, superconducting coils, and/or fixedmagnets. Magnet 42 may include a multi-pole magnet is used to generate a“true” minimum field configuration (as described below). In someembodiments, this may be implemented using fixed magnets, althoughelectromagnets or other magnets could be used. A superconducting centralmagnet 42 is convenient when superconducting magnets 36 and 38 are used,since the area must be cooled close to absolute zero.

Exciter system 44 excites the electron cyclotron resonance of electronsin chamber 40. In some embodiments, to produce ECR excitation, theexciter system 44 introduces microwave energy into the ionizationchamber 30 directly. In typical embodiments the center field magneticregion 40 between the two magnetic mirror fields 32 and 34 issubstantially uniform (constant magnetic field) although a non-uniformmagnetic field will operate. Preferably, the rear part 47 of theionization chamber 30 includes a connection 48 to a gas source 50, whena gas to be ionized is introduced into the system. In other embodiments,the gas can be introduced anywhere a convenient connection can be made.A perforated plate 52 separates the chamber 30 from a vacuum pump 54 tomaintain a slight gas pressure within the chamber 30 and produce a beam56 of the desired ions from the plasma 57 confined between mirror fields32 and 34.

The ECR exciter system 44 provides an electric field that couples to theelectron cyclotron motion of electrons in chamber 30. Since the electroncyclotron frequency is generally high, the ECR drive tends to be in themicrowave frequencies. For these frequencies, wave guides provide themost efficient coupling. ECR coupling, however, is not limited to waveguides, and can be accomplished in other ways, such as cavity modeexcitation, optical drive, etc.

If a gyrotron, or other circular wave guide device, is used as an ECRsource, good performance will typically be obtained when the rotationdirection of the wave within the wave guide is matched to the rotationdirection of the electrons in the magnetic field 40. The position of theECR drive output 55 and gas feed 48 can be optimized so that plasma isprimarily produced between the two magnetic mirror fields 32 and 34. Insome embodiments, this increases the overall efficiency and minimizesthe plasma production in the rear part 47 of the chamber 30, which cansimplify the microwave feed system.

The frequency and power in the ECR drive system 44 are related to theplasma density produced. Higher frequency and power both typicallycorrespond to a higher plasma density. The optimal power and type of ECRsource may be adjusted for each type of ion.

The substantially uniform central magnetic field 40 between the twomagnetic mirrors 32 and 34 will operate for a wide range of lengths. Theoptimal length may be readily determined experimentally for each ion,selected final ionization state, beam intensity, beam pulse length, andECR power. Increasing the length of the central magnetic region 40increases the region over which hot electrons are confined, and thusincreases the potential for ionizing collisions. Making this regionlarger increases the ionization, but at the expense of increasing thetime it takes to form a stable plasma. Optimally, a pair ofsuperconducting magnets 36 and 38 are used. Such magnets may not allowfor significant variations in the length of the magnetic field 40,because they are not easily relocated. For production of He⁺⁺, this istypically not an issue. But for production of other highly charged ions,more easily movable magnets may be used to allow adjustment the magneticfields.

In some embodiments, the central magnetic field 40 is chosen to matchthe ECR frequency of the microwave source 44. The exact values of themirror fields 32 and 34 are not critical to the operation of the system10, but may have a large impact on system efficiency. In someembodiments the rear mirror field 32 is higher then the front mirrorfield 34 (e.g. as shown in FIG. 4). A beam may be formed by allowingions to leak out of the mirror fields 32 and 34. By making the rearmirror field 32 higher than the front mirror field 34, most of the ionlosses, which form the multiply ionized particle beam 56, are throughthe front mirror field 34. In other embodiments, mirror fields 32 and 34may be of equal or substantially equal strength.

The exact value of the front magnetic minor field 34 can be chosen froma wide range of values, and is generally close to a value of twice thecentral field 40. In other embodiments it may be three, four, five, ormore times that of the central field. Using a higher value of the frontfield 34 increases the confinement of the ions and electrons, but cancause instabilities in the flow of the plasma 57. Using a lower valuefield decreases the fraction of ions trapped between the mirror fields32 and 34. The optimum value depends on the ion, charge state, gaspressure, beam intensity, and ECR power. The exact values may bedetermined experimentally in each instance.

In order to understand the operation of the system 10, it is helpful tounderstand how a magnetic mirror 32 or 34 works. Magnetic mirroringoccurs when a charged particle moves from a region of low magnetic fieldto a region of high magnetic field. The magnetic moment of the particleis an adiabatic invariant of the motion:

$\mu \equiv \frac{{mv}_{\bot}^{2}}{2B}$

An adiabatic invariant remains invariant so long as the rate of changeof the parameters is “slow”. “Slow”, means that the magnetic field andthe perpendicular velocity change slowly over one cyclotron period. Intypical embodiments of the magnetic minors described herein, this isgenerally an excellent approximation, except possibly during extractionof the beam 56. The invariance of the magnetic moment indicates that ifthe particle moves from a region of small magnetic field to a region oflarge magnetic field, the perpendicular velocity must increase. Byconservation of energy, this means that the parallel velocity mustdecrease. Thus, if a particle with a given perpendicular velocity movesfrom a region of low magnetic field to a region of sufficiently highmagnetic field, the parallel (axial) velocity will go to zero, therebystopping the particle. As is familiar to those skilled in the art, amore through analysis of the particle dynamics shows that, in fact theparticle will be reflected.

By combining the magnetic moment invariant with the conservation ofenergy,

$E = {{\frac{1}{2}{mv}_{\bot}^{2}} + {\frac{1}{2}{mv}_{\parallel}^{2}}}$

a simple set of equations governing the flow of a particle from magneticfield B₁ to magnetic field B₂ can be derived:

$v_{\bot 2}^{2} = {v_{\bot 1}^{2}\frac{B_{2}}{B_{1}}}$$v_{\parallel 2}^{2} = {v_{\parallel 1}^{2} + {v_{\bot 1}^{2}( {1 - \frac{B_{2}}{B_{1}}} )}}$

When a particle travels from a low magnetic field to a high magneticfield, the second term in the parallel velocity equation can benegative. If it is sufficiently negative the particle will stop and bereflected. Therefore, if particles are moving from one magnetic field toanother, the reflection depends on the ratio of the perpendicular toparallel velocity of the particle. Specifically, the particle will bereflected at some point when:

$\frac{v_{\parallel 1}^{2}}{v_{\bot 1}^{2}} < ( {\frac{B_{2}}{B_{1}} - 1} )$

the non-reflected particles can be visualized as a cone 58 in velocityspace, as shown in FIG. 5.

Generally magnetic minors fields, such as magnetic mirror fields 32 and34 leak. Particles in the loss cone 58 leak out of the front mirrorfield 34 (or the back mirror field 32). Particles that are not in theloss cone 58 are eventually scattered into the loss cone 58. The systemsdescribed herein, in various embodiments, rely on this scattering tomove the particles into the loss cone 58 that will then pass through thefront magnetic mirror field 34 and form a source of ions.

Referring back to FIG. 2A, during source operation microwaves are usedto excite the ECR in the central region 40 in chamber 30 of the source.This generates hot electrons that ionize the background gas. For He⁺⁺production, the preferred electron energy is around 200-300 eV. Forother atoms, the preferred electron energy may easily be experimentallydetermined by the energy required to produce the desired charge stateand/or the peak of the cross sections involved.

Considering first the production of alpha particles (He⁺⁺) the hotelectrons generate mostly He⁺ and some small amount of He⁺⁺. Some of thegenerated He⁺ is trapped between the magnetic mirror fields 32 and 34and undergoes a second collision forming He⁺⁺. Gradually, the He⁺⁺ andHe⁺ are scattered into the loss cone 58 where they leak out, primarilythrough the front mirror field 34, forming the beam 56 of Ne and He⁺⁺.Generally the description focuses around alpha particles (⁴He⁺⁺), butthe same discussions apply equally to helium-3 ions (³He⁺⁺) or otherdoubly ionized ions.

The plasma beam 56 of He⁺ and He⁺⁺ in a ratio (determined as the ratioof the beam current of He⁺⁺ to total beam current) of up to 84% He⁺⁺ ormore leaking from the front mirror field 34 is producible using an ECRsystem 44 only, is accelerated by a extractor 59 which may include asequence of electrodes and focusing elements to form the particle beam56. In cases where it is desirable to transmit the beam 56 to a magneticfield free region, the extraction system can be designed to make surethat particles remain adiabatic until the particles are out of themagnetic field 34.

If the plasma flow out of the magnetic field zone remains adiabatic, themirror relations can be applied. As the particles travel from the highmagnetic field to the low magnetic field, perpendicular energy isconverted to axial (parallel) energy. This keeps the emittance of thebeam 56 low during the particle extraction. A non-adiabatic extractionof the beam 56 results in perpendicular energy of the beam 56 beingretained and the extracted beam 56 has larger emittance.

There are four known major sources of particle losses in the plasmasystem 60 of the present invention. These are: recombination, chargeexchange, radial diffusion, and loss cone scattering (axial diffusion).

In typical embodiments, Recombination is not a significant effect.Generally, the electrons in the plasma system 57 are at a very highenergy. As a new electron is liberated in an ionizing collision, itrapidly gains energy. Therefore, recombination between the energeticelectrons and the ions is not significant.

Charge exchange affects only the multiply charged ions. If an electronis transferred from He to He⁺, the result is the same number andcomposition of ions, that is, the He becomes He⁺ and the He⁺ becomes He.If an electron is transferred from He to He⁺⁺, however, the result istwo He⁺ ions, so a He⁺⁺ ion was lost. In the case of the devicesdescribed herein, the ion energy can be sufficiently low that chargeexchange is not a significant problem.

Radial diffusion is not an issue if the central magnetic field 40 islarge. If the cyclotron orbit of an ion is small compared with the sizeof the ionization chamber 30, radial diffusion is very slow andparticles are scattered into the loss cone 58 faster than they diffuseradially.

In typical embodiments, scattering into the loss cone 58 is the primaryloss method for particles. The system 10 requires this scatteringprocess in order to generate the beam 56 from the plasma 57. Loss conescattering of He⁺⁺ is desirable as this forms the extracted ion beam 56.Loss cone scattering of He⁺, however, is not desirable as it causes He⁺to enter the beam 56, thus increasing the percentage amount of He⁺ inthe beam 56. He⁺ ions in the beam 56 can be separated from the He⁺⁺ ionsusing a mass ion filter 61, but this decreases the beam intensity,increases the emittance, and decreases the overall beam efficiency.

The hot electrons generated by the ECR source 44 have a non-isotropicdistribution, with the perpendicular energy being much larger then theaxial energy. Ions generated by the collisions with the electrons alsohave a non-isotropic distribution with more of the energy perpendicularto the magnetic field 40 than parallel. Given a mirror ratio near 2(B_(mirror)/B_(central)), somewhat more than half the formed He⁺ isconfined by the mirror fields 32 and 34, and somewhat less than half theHe⁺ is not confined and leaves the mirror fields 32 and 34 on the firstpass. Some of the initially unconfined particles exit from the rearmirror field 32 and the rest exit from the front mirror field 34.Depending on the particle densities and temperatures, geometricconsiderations, and some other parameters, the produced beam 56 willtypically be between 50-90% He⁺⁺ and 50-10% He⁺. The exact ratio of He⁺to He⁺⁺ in the generated beam 59 depends on a complicated set ofrelations between gas density, ECR power, source geometry, and magneticfield geometry. The exact ratio can be determined experimentally andoptimized to produce a desired beam ratio 56. As noted above, beamratios of 84% or greater have been experimentally demonstrated usingdevices of the types described herein.

The ratio of highly multiply ionized particles can be increased by usingan ICR (Ion Cyclotron Resonance) exciter system 62, although for He⁺⁺,it may not be needed. This system 62 uses antennae 68 in the chamber 30between the mirror fields 32 and 34 to emit at the radiation properfrequency to couple energy into the ion cyclotron resonance of He⁺ ions,thus coupling energy into the perpendicular motion of the He⁺ ions. Ingeneral, the axial (parallel) velocity of the particles remainsunchanged by ICR excitation. Increasing the perpendicular energy pushesthe driven particles out of the loss cone 58. In some embodiments, byusing ICR excitation, the scattering rate of He⁺ into the loss cone 58can be reduced to nearly zero.

In reality, the He⁺ ions cannot be kept out of the loss cone 58indefinitely. Given sufficient time, particles will be scattered intothe loss cone 58. This scattering basically is converting some of theparticle's perpendicular energy into parallel energy. The ICR excitationcan then add more perpendicular velocity and push the particle back outof the loss cone 58 again, but eventually, the parallel energy will getsufficiently high that the particle will escape the mirror fields 32 and34.

The goal is not to keep ions out of the loss cone 58 indefinitely, butrather just long enough to undergo a multiple ionizing collisions. Whenthe system 10 is operated at a high plasma density, these multipleionizing collisions occur faster than scattering into the loss cone 58.

When the ICR excitation is used, the system 10 operates as follows.Microwaves excite the ECR in the central magnetic region 40 of thechamber 30, which generates hot electrons. These electrons ionize thebackground helium gas producing mostly He⁺ ions, but also some He⁺⁺ions. The ICR system 62 excites the He⁺ resonance in the centralmagnetic region 40. The He⁺ ions are trapped between the two magneticmirror fields 32 and 34 where a second collision with an electron causesa second ionization to produce He⁺⁺. The ICR excitation does not coupleto the He⁺⁺ ions, which have twice the cyclotron frequency. The He⁺⁺ions are scattered into the loss cone 58 where they exit the chamber 30as the ion beam 56. In some embodiments, most of the He⁺⁺ exits via thefront mirror field 34, which is lower. In some embodiments, the heightof the hack mirror field 32 should be as high as possible, or at leasthigher than the front mirror field 34. However, system 10 may operateeven when front mirror field 32 is equal to or substantially equal toback mirror field 34

In some embodiments, the ICR excitation causes the density of the plasmato increase until losses balance production. In the limit, where the ICRexciter 62 can hold the He⁺ out of the loss cone 58 indefinitely, theplasma density will increase until the production of H⁺ is equal toproduction of He⁺⁺, which equals the rate that He⁺⁺ is scattered intothe loss cone 58.

Most of the above examples have focused on helium. Helium has only twocharge states no it is easy to see how system 10 can produce a highdensity ion beam 56 of He⁺⁺. The same technique can also be used toproduce multiply ionized ions in a selected final ionization state ofalmost any other atom, especially when the ICR system 62 is used.However, when working with other atoms (e.g. those with more than twoionization states), several issues are notable.

First, depending on the ionization state and the atom required, it maybe necessary to increase the electron energy of the ECR heatedelectrons. This can be done by increasing the power in the ECR source 44and/or by decreasing the cooling effects on the electrons. Under thecorrect conditions one may obtain electron energies as high as 600 to1000 keV. In order to obtain very high electron temperatures, it may benecessary or desirable to add a radially confining multipole field tothe center region 70 of the magnet system, creating a “true” minimummagnetic field configuration. In some embodiments, a radially confiningmultipole magnet 72 (e.g. a hexapole, or higher order multipole magnet)may be used. This may have some real advantages if an ICR exciter system62 is used. As described in more detail below, the higher ordermultipole magnet 72 localizes the field effects to the outer radial edgeof the plasma 57 and leaves the central part of the plasma 57 (locatedproximal to axis A) unaffected. The “true” minimum magnetic fieldconfiguration provides a form of insulation between the plasma 57 andthe wall 76 of the chamber 30 and makes it easier to obtain hightemperature electrons.

Second, if the ICR exciter system 62 is used, there is a question ofwhat ICR frequency to use. When there are several ionization chargestates available, so there will be several potential ICR exciterfrequencies:

$\frac{1{eB}}{M},\frac{2{eB}}{M},\frac{3{eB}}{M},\frac{4{eB}}{M},\ldots$

In some embodiments, one frequency is chosen for excitation. Generally,exciting the lowest ionization state provides the most increase inproduction of any higher states. It is also possible to excite multiplestates, or all states. For example if the desire was to produce O⁺⁸,useful in treating inoperable tumors, an ICR excitation system could beprovided with multiple antennae that excite the ICR resonances of O⁺,O⁺⁺, O⁺³, O⁺⁴, O⁺⁵, O⁺⁶, and O⁺⁷, thus preferentially holding all oxygenions other than O⁺⁸ within the chamber 30.

The system 10 includes a positive source 78 to bias the chamber 30 athigh potential in order to accelerate the ions extracted. Therefore anumber of insulators 80 are necessary to allow the system 20 to bebiased at different voltages and to electrically isolate the chamber 30to provide operator safety.

There are a number of different ways to implement insulator systems.These include, but are not limited to the embodiments of system 10 shownin of FIGS. 2A, 2B, 2C, and 2D. The configurations shown in FIGS. 2A and2B are just variations of each other with insulators 80 used toelectrically isolate the vacuum pump 54, the ECR source 44 and the atomsource 50. The system shown in FIG. 2C is significantly different inthat the entire outer wall 86 of the chamber 30 is biased at ground. Aninternal bias liner 88 is used to control the plasma bias and thus theextraction energy of the ions. In terms of fabrication, in someembodiments this may be somewhat more complicated, but may providegreater operator safety in that it is more difficult for an operator tocome in contact with the high voltage. With an inner bias liner 88, theliner 88 could be placed either inside or outside of the ICR antenna 90.In some cases, it may be possible to use the ICR antenna 90 itself as abias liner 88, but if the bias liner 88 is placed inside the ICR antenna90, it must contain at least one slit to prevent shorting out the ICRdrive.

FIG. 2D shows a variation of system 10 using a non-conducing vacuum wall80 where the ICR antenna 90 external to the vacuum system. A Faradayshield 98 is used as a bias liner inside the vacuum system.

An external antenna design can be generalized to work with mostantennas. In most cases an insulating chamber wall can be used. Theantenna system can be located external to the vacuum system. A biasliner containing slit(s) can be used inside the chamber to control theplasma bias without interfering with the ICR excitation.

As shown in FIGS. 6A and 6B, an ICR exciter system 62 includes an RFdrive system 96, an antenna 90, and a tuning system 100. The goal is togenerate an electric field that will couple to the ion cyclotron motion.An electric field rotating in the same direction as the ions providesthe highest coupling, but other combinations such as linear or radialelectric fields also work. Generally the ICR frequencies are in the RFrange and the antenna 90 is fed from coaxial lines 102. Acapacitor/inductor network normally is used within the tuning system 100to match the antenna 90 with the driver system 96. In typicalembodiments, the magnetic field in the region where the ICR exciter isapplied should be relatively constant so that the cyclotron frequency ofthe ions is well defined. Central uniform field region 40 meets thisrequirement. Depending on how the antenna 90 is implemented and how theinsulator system is implemented, the antenna 90 may be at high voltage.Coupling between the antenna 90 and RF drive system 96 can be providedusing a transformer or capacitors in order to provide isolation betweenthe systems.

A number of different antenna systems such as antennae 90, can be usedfor the ICR exciter 62 These include, but are not limited to: cavityexcitation, capacitor plates, split-ring, and filer. Cavity excitationsimply couples to the cavity mode of the chamber 30 using a loop (notshown) or some other type of exciter.

The optimal antenna design may depend strongly on the specific ion andcharge state desired. For production of multiply charged ions other thandoubly charged ones, it may be desirable to drive the antennae atmultiple frequencies.

Capacitor plate antennas can be either linear (FIG. 6A) or circulardrive (FIG. 6B). In the case of linear drive the two plates 104 and 106are driven to generate an oscillating electric field. In the case of acircular drive, vertical plates 108 and 110 are driven 90° out of phasewith the horizontal plates 104 and 106, generating a rotating electricfield. In other embodiments, other phase angles may be used, therebygenerating elliptical drive radiation. Note also that although the termsvertical and horizontal are used here for convenience to describe therelative positioning of the plates, the antenna plates may be orientedarbitrarily in chamber 30. The exact structure of the plates isunimportant, other than that they provide an electric fieldperpendicular to the magnetic field 40. In some embodiments, capacitorplate antenna (or other antenna type) may be used in exciter system 62to produce output at multiple frequencies

Referring to FIG. 7, a split-ring antenna 111 consists of a coil of wire(or tubing to allow cooling) 112 wrapped around a Faraday shield 114.The Faraday shield 114 prevents the helical electric field of the coil112 from reaching the plasma 57. The lengthwise slit 116 in the metal ofthe Faraday shield 114 allows a mostly linear component of the electricfield to reach the plasma 57, which couples to the ion cyclotronresonance. The actual electric field is more like radial arcs comingfrom the slit 116, but this couples to ion motion with about the sameefficiency as a linear drive system.

In cases where an internal bias liner is used, e.g. as shown in FIG. 2C,it is possible to use the Faraday shield 114 as a bias liner inside theICR exciter system 62. A variation of this arrangement, as shown in FIG.2D, is to use a non-conducing vacuum wall insulator 80 and place the ICRantenna external to the chamber 30, and use the Faraday shield 98 as abias liner inside the chamber 30.

An external antenna design can be generalized to work in mostconfigurations. In most cases, the chamber 30 can include an insulatingchamber wall 80 so that the ICR antenna 68 can be located in a region ofambient pressure, outside of the chamber 30. A bias liner 98 containingone or more slits 116 (as shown in FIG. 7) can be used inside thechamber 30 to control the plasma bias without interfering with the ICRexcitation.

Referring to FIG. 8, a filer antenna 124 contains a number of helicalconductors, 126 and 128 shown, in which currents are driven. Dependingon the type of filer, either a linear drive field or a rotating (i.e.circular or elliptical) drive field is generated. For a rotating drivefield, as shown, there are actually two filers 130 and 132 that areconstructed perpendicular to each other having helical conductors 126and 128, and 135 and 136. The two filers are driven 90° out of phase togenerate a rotating electric field. A simple filer antenna would haveonly one of the two filers 130 or 132.

In addition to the other variations in the ICR antenna systems 60discussed above (cavity excitation, capacitor plates, split-ring, andfiler) an untwisted filer antenna 140 can be used. As shown, untwistedfiler antenna includes two filers 141 and 142. In some embodiments asinge untwisted filer may be used. In this case, one of filers 141 and142 would be omitted.

The bi-filer antenna 124 is basically a twisted set of current carryingwires. The wires on opposite sides of the plasma 57 carry current inopposite directions. These wires combine to generate a magnetic field inthe center of the plasma 57. As the current oscillates, the generatedmagnetic field oscillates, and induces an electric field in the centerof the plasma 57. A single filer antenna generates a linearly polarizedexcitation and the bi-filer antenna typically generates a rotatingexcitation field (circularly or elliptically polarized). Generallyinductive antenna systems (such as the filers) have advantages overelectrostatic antennas (such as capacitor plates). This is because thehigh density plasma 57 tends to screen out the electric field generatedby electrostatic antennas, thus such antennae primarily couple to theplasma 57 only at the outer edge of the plasma 57. Inductive antennaedrive though an induced electric field that is generated by anoscillating magnetic field. The magnetic field can pass through theplasma 57 and thus the drive field is located everywhere in the plasma57, and generally is peaked on the axis of the chamber 30.

Typically a filer antenna 124 has a twist in it to prevent chargeseparation in the plasma 57. In the present invention, the twist is notneeded. The short length of the source allows the particles at the endof the plasma 57, where the drive field is weak, to provideneutralization, thus charge separation is not a large problem. Furtherneutralization is provided by plasma rotation, which prevents theantenna, such as bi-filer 124, from driving only over one part of theplasma 57. The plasma rotation is due to the slight non-uniformity ofthe plasma 57 as ions and electrons are lost at slightly differentrates, resulting in a slight charge imbalance that equalizes these twoloss rates (ambipolar potential). This charge imbalance gives rise to aradial electric field, which combined with the axial magnetic fieldgives rise to plasma rotation.

The untwisted-filer antenna 140 has advantages that it will couple tothe ions going both directions in the source. The twisted-filter antennaimposes a Doppler shift on the ICR drive field. This means the drivefield couples to particles with a cyclotron frequency given byω±k_(z)v_(z) (where the sign is determined by the direction of theantenna twist relative to the direction of ion cyclotron rotation, andk_(z) is determined by the structure of the filer). The twisted-filercan be matched to particles going one direction in the device (saypositive-z), but not the other direction, since the sign of the axialvelocity will change. The untwisted-filer has k_(z)=0, thus it willcouple to particles going both directions in the device. This allows theICR exciter to couple to more of the plasma.

Referring to FIGS. 10A and 10B, system 10 may be operated in resonant(FIG. 10A) or sub resonant (FIG. 10B) ECR modes. In the resonant mode,ECR source 44 produces microwaves are resonant with the ECR motion ofelectrons the uniform field 40 (resonant zone 200 located between thetwo mirrors fields 32 and 34 as shown in FIG. 10A). This zonecorresponds to a cylindrical volume about axis A in region 70 of chamber30. This arrangement provides the highest coupling between the electronsand the microwaves.

The general requirements on the uniformity of the central field for theresonant mode can be expressed as a relation between the electronconfinement time and the electron de-correlation time. If an electron isplaced in a uniform magnetic field it will orbit about the field withthe cyclotron frequency given by

$\omega_{ce} = {\frac{eB}{m}.}$

If the electron motion is driven by an ECR drive generating a rotatingelectric field that rotates in the same direction as the electron, theelectron can gain energy. If the drive frequency (ω_(ECR)) exactlymatches the electron cyclotron frequency the electron will continue togain energy until relativistic corrections to the electron motion becomesignificant. In typical embodiments this is not a significant issue asrelativistic corrections will be come significant when the electronenergy becomes a significant fraction of the electron rest energy. (Theelectron rest energy is 512 keV and, for many embodiments, targetelectron energies are 200-300 eV for alpha particle production, andabout 1 keV for production of C⁶⁺).

If the drive frequency does not exactly match the electron cyclotronfrequency, then the electron will first gain energy then loose energy,and then gain it again. In fact, when the electron looses energy it willreturn to the same initial conditions as before it was accelerated bythe ECR drive. The time scale of this loss and gain of energy is given,in terms of the ECR frequency ω_(ECR) by

$\tau_{DC} = {\frac{\pi}{{\omega_{ce} - \omega_{ECR}}}.}$

The gain (or loss) of energy of an electron in an off-resonant ECR drivefield is also limited by

${\Delta \; K_{\max}} \approx \frac{m\; \xi^{2}}{2( {\omega_{ce} - \omega_{ECR}} )^{2}}$

where ξ is the normalized electric field eE/m.

In some embodiments, the field is not completely uniform. In such acase, the cyclotron frequency can be replaced with an average cyclotronfrequency experienced by the electron. Or more accurately an averagevalue over all the electrons of the average cyclotron frequencyexperienced by each electron.

Given these conditions we can express a sufficient condition on theuniformity of the field as the de-correlation time must be longer or onthe order of the electron confinement time in the device. For the onresonant mode, when this condition is met, the field may be consideredto be substantially uniform.

In some embodiments field 40 is uniform to 1% or less, 5% or less, 10%or less over a region extending axially 5 cm, 10 cm, 15 cm, 30 cm orgreater, while the mirror-to-mirror distance is 60 cm.

In some cases, operation in the resonant mode may result in tooenergetic electrons. For example, in the case of formation of He⁺⁺, thepeak of the cross sections for all formation methods is between 200-300eV. Given sufficient power and coupling, electron temperatures wellabove 10 keV can be generated. These high energy electrons are notuseful for the formation of the He⁺⁺, and tend to produce unwantedX-rays. The electron temperature can be controlled by manipulating themicrowave power, gas pressure, the length of the resonant zone(s) andelectron confinement time.

An alternative system, as shown in FIG. 10B, for controlling theelectron temperature is to adjust the magnetic field in the centralregion 40 such that the ECR drive is detuned from the uniform field 40.This is referred to herein as the sub-resonant mode. This mode restrictsthe microwave coupling to zones 180 and 182 localized on each end of thechamber 30 adjacent the mirror field zones 32 and 34 (in contrast to thelarge cylindrical volume in which coupling occurs in resonant modeoperation). The lower the central field 40, the smaller these zones 180and 182 become. This method has the advantage that high microwave powerin this configuration corresponds mostly to high electron (and plasma)density and not to high electron temperature. This method can be moreefficient for production of low to moderate ionization states (such asHe⁺⁺).

In this mode of operation there are two small ECR sections 180 and 182located between the uniform field region and the magnetic mirrors.Particles are not in these zones long enough for de-correlation to be asignificant issue. Electrons pass through the ECR zone, and depending onthe phase of the particle relative to the ECR drive phase, the particlewill gain or loose some energy in the zone. Because the phase at whichthe vast majority of electrons encounter both ECR zones is notcorrelated, they gain or loose energy each time they pass through theECR zones. This leads to a stochastic heating process (similar to randomwalk) that leads to the gradual gain of energy (i.e. gradual ascomparison to the resonant mode using similar operating parameters). Forthis process directly there are not requirements on the field uniformityof the central field, but the limitations on plasma stability stillapply.

In some embodiments with this configuration the relation between thecentral field and the ECR frequency is significant. If these two matchtoo closely, then one cannot consider the electrons to leave the ECRzone, and the entire central region appears to be one large ECR zonethat is off-resonance. If this is the case the performance of the systemis very poor, as the energy gained by the electrons is limited by therelation given above. Further the de-correlation time is short, so theelectrons gain and loose energy rapidly leading to poor confinement.

If the central region corresponds to a magnetic field that issufficiently far from the resonance condition, then the energy that canbe gained or lost by an electron crossing the zone is limited by therelations above. Further, if the central region is sufficiently far fromthe resonant condition, other effects dominate the transit through thecentral region. This allows the electron phase to be effectivelyrandomized between the two ECR zones. This reduces or eliminates thenumber of particles that are consistently poorly phased matched betweenthe two zones.

The ICR exciter system 62 can be used as there still will be a uniformmagnetic field 40 in the center of the chamber 30, but the ECR zoneswill be located only adjacent the zones of the mirror fields 32 and 34.In such cases, the ICR frequency is decreased slightly to match thelower resonant field. An added advantage is the mirror ratios on thefront and back mirror fields 32 and 34 are increased somewhat as thecentral field 40′ is lowered.

FIG. 15 illustrates both resonant and sub resonant modes of operation.FIG. 15 is a plot of total extracted beam current as a function becentral magnetic field (at constant ECR drive frequency of 18 GHz) usingsmall aperture. The sharp peak located at approximately 0.638 Tcorresponds to resonant mode of operation. The broad flat peak around0.5 T corresponds to the sub-resonant mode of operation.

Note from the graph it may appear that the sub-critical mode ofoperation yields more current and thus may be better, but this can bemisleading. The data was taken by varying only the central field, thusthe mirror ratio, which is strongly tied to plasma production, is notconstant across the graph. Also the beam composition is not plotted hereso the ratio of He⁺⁺ to He⁺ also varies along the graph.

The region between 0.635 T and 0.56 T, neither mode fully applies.Clearly close of 0.63 T the electron de-correlation time is short, andthe maximum energy obtained the electrons is too low for the formationof He⁺⁺. As one approaches the 0.6 T, the ECR zones have moved out fromthe central region, toward the higher field, but the zones may be toolarge and too well correlated to lead to an efficient stochastic heatingprocess.

FIG. 16 shows time-of-flight mass spectrometer data for the resonantmode of operation. The horizontal axis represents time; the data near3.5 μs corresponds to He⁺⁺ and the data near 5.5 μs corresponds to He⁺.The vertical axis indicates the central magnetic field. Note the He⁺⁺production is flat between 0.636 T and 0.639 T. This region correspondsto the electron de-correlation time being longer then the electronconfinement time so electrons are lost before they can decelerate.

The uniform field region also has another advantage other then justcoupling energy to the electrons or ions. In some embodiments, mirrordevices are unstable to a number of instabilities driven by thecurvature of the magnetic field. In particular, the shape of the fieldin the region between the uniform field and the magnetic mirror can bevery unstable. In this region the combined drift of the particles in thecurved magnetic field is given by

$\overset{->}{v} = {{{\overset{->}{v}}_{R} + {\overset{->}{v}}_{\nabla B}} = {\frac{m}{q}\frac{{\overset{->}{R}}_{C} \times \overset{->}{B}}{R_{C}^{2}B^{2}}( {v_{\bot}^{2} + {\frac{1}{2}v_{\parallel}^{2}}} )}}$

where R_(C) is the radius of curvature of the magnetic field. Thesedrifts cause ions and electrons to drift in opposite directions. Theresulting electric field generated by the change separation gives riseto a radial E×B drift

${\overset{->}{v}}_{E \times B} = \frac{\overset{->}{E} \times \overset{->}{B}}{B^{2}}$

that can lead to radial diffusion. When the magnetic field is curvedtoward the plasma (concave) the resultant drift causes outward transportand loss of the particles. This is often referred to as “bad” curvature.On the other hand, when the magnetic field is curved away from theplasma (convex) the resultant drift causes inward transport andconfinement of particles. This is often referred to as “good” curvature.

In a simple magnetic mirror, the particles spend much more of their timein the regions of “bad” curvature then in the regions with “good”curvature and this leads to rapid radial loss of particles.

In the systems described herein, the uniform field regions greatlyincrease the stability of the plasma and provide for ion confinementtime that is comparable to the time required to remove the second (ormore) electron(s) to form ions in the selected final state.

The increased stability is provided by a number of factors. First, theuniform sections have essentially no curvature so they decrease theoverall time particles spend in the regions of “bad” curvature. Thereare thresholds associated with the instabilities that lead to transport.Clearly curved magnetic field driven instabilities will not grow if theaverage magnitude of the drifts are smaller then thermal transportdrifts. Second, the uniform field region contains a large fraction ofthe plasma. This region provides a charge reservoir that damps out thechange separation caused by the curved magnetic field drifts. Basicallythis allows charge to flow along the axis and neutralize the changeseparation caused by the “bad” curvature region. Third, the uniformregion disconnects the two regions of “bad” curvature. Thusinstabilities growing on one end of the device generally cannot coupleto instabilities growing on the other side of the device due toinconsistent phase shifting by particles traveling from one side of thedevice to the other.

In some embodiments, requirements on the field are on the order of 5-10%uniformity over the majority of region 70. Stability may be more of anissue in the sub-critical mode because of the potentially higher mirrorfields which reduces the threshold for instabilities.

Referring to FIGS. 14 and 14A, in some embodiments, (e.g. for generationof very highly ionized ion species and/or for generation of very intenseion beams) it may be helpful to add a radial surface confinementmagnetic 76 to the system 10. Confinement magnet 76 produces radialconfinement field 184 turns the axial minimum field configuration into amore complete minimum field confutation, by adding a generallyincreasing magnetic field as a function of radius. Note that a trueminimum magnetic field configuration cannot be generated (such a staticconfiguration would violate Maxwell's laws). Configurations referencedto in the art as “true” magnetic minimum configurations are just partialminimum magnetic fields. All of these types of configurations containcusp regions where the field does not increase as a function of radius.The size, shape, and location of these regions distinguish thesedifferent minimum magnetic field configurations.

The surface confinement magnetic field increases the confinement time ofthe electrons in the system 30. This increases the electron density inthe system 30, as well as the electron temperature (energy), as theelectrons are in the ECR drive field longer. Higher electron densitycorresponds to more ionizing collisions with neutrals and ions. Higherelectron energy corresponds to the ability to generate higher ionizationstates. This is not useful for He⁺⁺, but could used for creating highlyionized states of other atoms.

In some embodiments, a hexapole fixed magnet system (not shown) is usedto generate a “true” minimum magnetic field configuration. The hexapolemagnets of alternating polarities create a field that penetratesradially well into the plasma 57, and limits the microwave couplingregion, as well as preventing the use of an ICR exciter system, becauseof the lack of a uniform magnetic field region.

As shown in FIGS. 14 and 14A, a higher order multipole field is used toproduce a surface confinement field 184 that would only affect the edges138 of the plasma 57, allowing for a broad ECR coupling region and useof an ICR exciter. A higher order multipole field can be introducedusing fixed magnets, but it can also be introduced using a series ofcurrent carrying wires 154, located around the source area In such acase, each wire 154 would carry current in the opposite direction to theadjacent wire 154, giving rise to an adjustable multipole magnetic field184. The strength of the current in the wires 154 determines themultipole field 184, which can be quite strong very close to the wires154, e.g. in region 185. The wires 154 used to generate the multipolefield 184 can be twisted or straight (as shown). The same wires 154 canbe used to produce the multipole field 148 and act as the ICR antennafor the “twisted” or “untwisted” filers. In such an implementation, thewires 154 would carry a DC and an AC component to the current and thusestablish both DC and AC components of the field 148. In someembodiments, the number of wires 154 used for a multipole may be high(more than the eight pairs shown), new phases could be introduced in theICR drive to increase the coupling efficiency, or some arrangement likeevery other wire 154 could carry an ICR drive signal.

Referring again to FIG. 2A, system 10 uses a microwave horn 55 to directthe microwaves for the ECR plasma production. In some embodiments, ahigher efficiency can be obtained using a cavity system (not shown). Thecavity both localizes the microwaves and the gas used in the system 10.Localizing the microwaves is good in that it increases the microwavepower density and thus the plasma density. Increasing the plasma densityincrease the number of ionizing collisions that can occur. It alsoreduces shielding and other problems from the microwaves.

Localizing the gas decreases the amount of wasted feed gas, generallynot a large expense, but less waste is less waste and some rare feedgases are relatively expensive. This also reduces arcing problems causedby high gas pressures in the chamber 30. If the feed gas is localized inthe cavity for the most part, it will not be in the antenna system, orthe insulators. The lower the gas pressure can be kept outside the gasgenerator, the better for suppression of arcs.

It is not necessary for the cavity to be fully closed in a gas tightsense. A number of holes can be placed in the wall as long as they aresmall compared to the wavelength of the microwaves. This will confinethe microwaves, but allow evacuation of the gas. Limiting the holes inthe wall controls the conductance to the rest of the vacuum system. Thiscan be used to keep the gas pressure high in the cavity but low in therest of chamber 30.

The gas source 50 can be operated using a wide variety of materialfeeds. In most cases these feed systems provide a neutral stream ofparticles from which to make a plasma and thus a beam.

In the case of alpha production, helium gas is used as a working gas. Inthe case of most other gaseous materials they can be used as a workinggas for the system. It does not matter if they are not simple atomicgasses. For example, if an oxygen ion source is desired, molecularoxygen can be injected into the source. The hot electrons will bothdissociate the oxygen and ionize it.

For materials that are not normally a gas there are several ways toinject the material into the source. One alternative is to inject a gascontaining the desired material. For example, carbon could be injectedusing CO or CO₂ as a working gas. In both cases, the plasma generatedwill contain both carbon and oxygen ions, thus the beam generated willcontain both types of ions. The source may be followed by a mass filterto eliminate the undesired ions.

An alternative would be to vaporize the substance into system 10. In acase such as calcium, it would be possible to simply heat solid calciumto vaporize it using an oven. Materials could also be vaporized bye-beam. This type of source is well suited to production of materialswith low melting points such as barium and calcium.

A laser system can be used to oblate a target, giving rise to neutralmaterial from which the plasma is formed. Such a system would fire alaser at a cooled target located in the chamber to produce neutrals. Theprime choice for the target location would be in the region 70 betweenthe two magnetic mirror fields 32 and 34. In some embodiments, thislocation makes the optics some what difficult so placement to the rearof the system, near the peak of the rear mirror, has a number ofadvantages. Other placements are workable, but may require more laserpower to generate sufficient neutral particles between the magneticmirrors 32 and 34.

One way to inject material is to use sputtering. Here the exiting ECRsource and magnetic mirrors may be used to generate a sputter source foralmost any solid material.

Referring to FIGS. 10A and 10B the ECR source may be adjusted to makeunconfined hot electrons at resonant zones 210 and 211 on both sides ofthe rear mirror. The non-trapped hot electrons generated on the frontand back of the mirrors are not useful for generating plasma 57. Theseelectrons are not confined and typically are quickly lost. Furtherresonance zones 210 and 211 are typically very narrow so there is notsufficient time for the electrons to gain a lot of energy. However, inembodiments featuring a sputtering source, one can use the unconfinedhot electrons on the back side of the mirror to form a sputter source.In such a case it would be desirable to tailor the magnetic field so thegradient is not so steep at zone 210 such that the resonance zone issufficiently large to produce the desired plasma density.

Referring to FIGS. 11, 12, and 13, a sputter source 212 works byallowing the hot electrons to ionize small amounts of gas to form aplasma in the vicinity of rear resonance zone 210. The sputter target isbiased with a large negative bias (e.g. 1-4 kV). This negative biasdraws ions from plasma formed and accelerates them to high energies.These ions then strike the sputter target 220 producing a number ofneutral particles. These neutral particles then pass through the hotelectrons in resonant zone 210. Some fraction of them are ionized,attracted by the negative potential, impact on the target 220, andsputter off more neutral particles. Some of the neutral particles passthrough the hot electrons and become ionized in the trapped resonancezone 200 (in resonant mode) or zones 180 an 182 (in sub-resonant mode)and form part of the particle beam.

The target material 220 does not have to be electrically conducting inorder to make a sputter target. For example, carbon can be used as atarget by simply placing it on a conducting surface 230. The conductor230 is biased to create the potential necessary to accelerate ions, butit is not necessary to bias the actual surface of target material 220.Conductor 230 my be isolated from the walls of chamber 30 by aninsulator 240.

In some embodiments, sputter source 212 may include fluid cooling pipes.Any suitable cooling technique known in the art may be employed.

In some cases the target material 220 does not sputter well. This can beexpressed as a sputter yield. The average number of neutral particlessputtered from the surface per single ion hitting the surface is thesputter yield. Materials that form good sputter targets have a yieldgreater then 1 (often significantly greater). If a material with a lowsputter yield is desired, a carrier gas can be used to increase theyield. Generally heavy gasses such as xenon are desirable because theytend to have high sputter yields on most targets and cause minimalproblems in the system. Some of the carrier gas will get ionized andfind its way into the output beam, but this can be minimized by correctchoice of the gas, geometrical arrangement, and/or filtered in theoutput beam.

In some embodiments, the geometry of a sputter source 212 is important.It is necessary that ions from the plasma can be accelerated into thesputter target 220, that neutral particles have a clear path into theplasma 57, and that the source does not block key things such as themicrowave access to the resonant zone. For example, sputter source 212may fall into one of two geometrical configurations. These are a sputtertarget 212 located on axis A (as shown in FIG. 11) and one located in anannulus (as shown in FIG. 12) or cone (as shown in FIG. 13) around axisA.

An ECR sputter source may be particularly well suited for generation ofmultiply changed ion beams from solid materials. As a practical example,there are applications for highly charged nickel ion beams. This sourceis particularly well suited to production of a nickel ion beam.

Referring to FIG. 11, in the case of an axially located target 220, thesputter target covers a small area along the axis of the ion source. TheECR microwaves are allowed to flow around the target, and may even beinjected off-axis to improve access.

In some embodiments, one may alternatively generate a sputter sourceusing ions from the main confined plasma. Biasing is used to attractions from the confined plasma to a sputtering target. For example, theions may be drawn backwards into a plate on the axis biased negativerelative to the plasma. In such embodiments, it is not necessary tocreate an unconfined plasma. In some embodiments, this may haveadvantages for microwave access at high plasma density.

The extraction system 59 passes the beam 56 through an extractionlimiter 65, forming the first electrode of the extraction system. Thebeam 56 is allowed to follow the magnetic field and expand as themagnetic field decreases. A focusing lens 64 is used to converge thebeam into the final limiter, which forms the boundary between the ionbeam source system 10 and the following systems (e.g. a beam filter oraccelerator).

By allowing the beam 56 to initially expand into a low field region thenaccelerating the beam to extraction energy, it is possible to transitionthe beam from the high field region magnetic field region 32, 34, and 40to a low field region without increasing the beam emittance.

In various embodiments, other suitable extraction systems and techniquesknown in the art may be employed.

The vacuum system 54 can be implemented using almost any standardpumping system. The high vacuum pumps should provide a base pressure atleast as low as 1×10⁻⁵ torr. During operation the gas or vapor from theatom source 50 can be bled into the system 10 at a higher pressure,providing high purity of the working gas.

There are a number of potential applications for high energy alpha(⁴He⁺⁺) or helium-3 (³He⁺⁺) beams. The most immediate applications arethe activation of target nuclei for the production of radio-isotopes.Due to short half-life and/or low production yield, it is necessary touse an intense beam in order to produce reasonable quantities of many ofthese radio-isotopes. Also, by using a target of very high purity, fewundesirable products are made so post processing (e.g. chemicalseparation) for isotope purity is minimized.

The following list indicates some of the possible target radio-isotopesthat can be produced from various targets using He⁺⁺ beams:

-   -   ¹⁸F, ¹²³Xe/I¹²³, ⁶⁷Ga, ¹¹¹In, ¹³¹Ba, ⁶⁸Ge, ⁸²Sr/Rb⁸², ⁸⁹Sr,        ¹⁵³Sm, ¹²⁴I, ²¹¹At, ¹⁴⁸Gd, ⁷⁶Br, ¹⁹⁹Tl, ¹⁰⁰Pd, ¹²⁸Ba, ^(117m)Sn,        and ²²⁹Th

Many of these radio-isotopes either are not currently produced or areonly produced in very limited quantities because of the difficulties intheir production. Using a ³He⁺⁺ or ⁴He⁺⁺ beam, however, many of theseradio-isotopes can be effectively produced. For example alpha (⁴He⁺⁺)particles can be used to produce desirable products as follows:

¹²C(α,n)¹⁵O¹⁵N(α,n)¹⁸F⁷⁹Br(α,n)⁸²Rb⁸⁶Kr(α,n)⁸⁹Sr⁹⁶Zr(α,n)⁹⁹Mo¹⁰⁰Ru(α,n)¹⁰³Pd¹⁰⁶Pd(α,n)¹⁰⁹Cd¹¹⁴Cd(α,n)^(117m)Sn¹²¹Sb(α,n)¹²⁴I¹²⁰Te(α,n)¹²³Xe(¹²³I)⁶⁰Ni(α,2n)⁶⁸Zn(⁶²Cu)⁶⁶Zn(α,2n)⁶⁸Ge(⁶⁸Ga)⁸⁰Kr(α,2n)⁸²Sr(⁸²Rb)⁸³Kr(α,2n)⁸⁵Sr¹⁰⁹Ag(α,2n)¹¹¹In¹²¹Sb(α,2n)¹²³I¹²³Sb(α,2n)¹²⁵I¹²⁹Xe(α,2n)¹³¹Ba(¹³¹Cs)¹⁹⁷Au(α,2n)¹⁹⁹Tl+2n¹⁹⁹HG(α,2n)²⁰¹Pb(²⁰¹Tl)²⁰⁶Pb(α,2n)²⁰⁸Po²⁰⁹Bi(α,2n)²¹¹At⁶¹Ni(α,p)⁶⁷Cu⁶⁴Ni(α,p)⁶⁷Cu¹⁰⁸Cd(α,p)¹¹¹In¹¹⁴Cd(α,p)¹¹⁷In(^(117m)Sn)¹²⁰Te(α,p)¹²³I¹²²Te(α,p)¹²⁵I¹⁶³Dy(α,p)¹⁶⁶Ho¹⁷⁴Yb(α,p)¹⁷⁷LuOther transmutations can occur to produce the same product, for example:¹⁴⁴Sm(α,gamma)¹⁴⁸Gd¹⁴⁷Sm(α,3n)¹⁴⁸Gd¹⁴⁷Sm(³He⁺⁺,2n)¹⁴⁸GdFor some reactions, production using alpha particles is greatly improvedrelative to other methods. Examples include¹⁰⁸Cd(α,p)¹¹¹In¹²¹Sb(α,2n)¹²³I⁸³Kr(α,2n)⁸⁵Sr¹⁵N(α,n)¹⁸F⁶⁶Zn(α,2n)⁶⁸Ge(⁶⁸Ga)¹⁵⁰Nd(α,n)¹⁵³Sm⁹⁶Zr(α,n)⁹⁹Mo¹²¹Sb(α,n)¹²⁴I¹⁹⁷Au(α,2n)¹⁹⁹TlSome isotopes that can be produced, e.g. in usable quantities,essentially exclusively with alpha (or He-3) particles. Exemplaryreactions include²⁰⁹Bi(α,2n)²¹¹At¹²¹Sb(α,n)¹²⁴I¹⁴⁴Sm(α,gamma)¹⁴⁸Gd¹⁴⁷Sm(α,3n)¹⁴⁸Gd¹⁴⁷Sm(³He,2n)¹⁴⁸Gd¹¹⁶Cd(α,3n)^(117m)SnIn some embodiments, a beam of deuterium ions may be used to drive thefollowing reactions:

³⁰Te(d,n)¹³¹I+ ²⁰⁰Hg(d,n)²⁰¹Tl ¹³⁰Te(d,n)¹³¹I

⁶⁴Ni(d,2n)⁶⁴Cu¹⁵N(d,2n)¹⁵O¹³²Xe(d,2n)¹³²Cs

¹¹⁰Cd(d,n)¹¹¹In ¹⁷⁶Yb(d,n)¹⁷⁷Lu

In some embodiments, a beam of protons (Hydrogen ions) may be used todrive the following reactions:

¹⁸O(p,n)¹⁸F ¹²⁴Te(p,n)¹²⁴I

¹²⁴Te(p,2n)¹²³I⁸⁵Rb(p,4n)⁸²Sr

²⁰¹Hg(p,n)²⁰¹Tl

Ion sources of the types described herein may also drive reactions suchas:⁶⁷Zn(³He,2n)⁶⁸Ga

¹⁹⁹Hg(³He,n)²⁰¹Tl ¹⁶O(³He,p)¹⁸F

⁶¹Ni(α,p)⁶⁴Cu⁶⁴Ni(α,p)⁶⁷Cu¹⁰⁸Cd(α,p)¹¹¹In¹¹⁴Cd(α,p)^(117m)In(^(117m)Sn)¹²⁰Te(α,p)¹²³I¹²²Te(α,p)¹²⁵I¹⁶³Dy(α,p)¹⁶⁶Ho¹⁷⁴Yb(α,p)¹⁷⁷Lu

As noted above, for treatment of radioactive waste, there are at leasttwo types of radioactive waste transmutation. The first is theproduction of useful products from waste material. Exemplarytransmutations which may be accomplished using the devices andtechniques described herein include:

²²⁶Ra(α,n)²³⁰Th+n. (²³⁰Th is a source for ²¹³Bi.)²³²Th+α→²³⁵U which is nuclear fuel.²³⁵U+α→²³⁸Pu which is used in nuclear fuel cells as a heat source and isin short supply.²³¹Pa+α→²³³Np+n-->²²⁹Pa-->²²⁵Ac which is a medical isotope. The ²²⁵Acdecay path is²²⁵Ac-α->²²¹Fr-α->²¹⁷At-α->²¹³Bi-beta->²¹³Po-α->²⁰⁹Pb-beta->²⁰⁹Bi.

Second, waste may be converted to a stable product. Exemplarytransmutations which may be accomplished using the devices andtechniques described herein include:

²⁵¹Cf++→²⁵³Fm+2n converts long lived Cf isotopes to short lived(approximately 3 days) Fm isotope, ²³⁷Np+α→²³⁹Am+n→²³⁵Np→²³¹Pa→ . . .→Pb.

Another other issue in treatment of nuclear waste is stimulated fissionreactions. In this case heavy radioactive nuclides are bombarded withalpha particles from a beam source of the type described herein. Thesenuclides undergo a stimulated fission reaction and fall apart into anumber of lighter fragments. Generally the fragments are stillradioactive, but have short half-lives and quickly decay to stableelements. Unlike many of the heavy nuclei, which are alpha and neutronemitters, these lighter ones are more likely beta and position emitters,which are easier to deal with. Intense (very intense) alpha beams areideal for this type of application.

^(99m)Tc is a metastable nuclear isomer of ⁹⁹Tc, indicated by the “m”.“Metastable” means that ^(99m)Tc does not change into another elementupon its decay. Instead ^(99m)Tc emits a 140 keV gamma ray that medicalequipment can detect from a body into which it has been injected.Accordingly ^(99m)Tc is well suited for the role of a medical tracerbecause it emits readily detectable 140 keV gamma rays, and itshalf-life for gamma emission is 6.01 hours. Over 93% of it decays to⁹⁹Tc in 24 hours. This short half life of the ^(99m)Tc allows forscanning procedures which collect data rapidly, but keep total patientradiation exposure low. ⁹⁹Tc is the ground state of ^(99m)Tc thateventually (half-life of 213 thousand years) emits a beta particle anddecays to ⁹⁹Ru, which is stable.

^(99m)Tc usually is extracted from so called “moo cows”, ^(99m)Tcgenerators which contain ⁹⁹Mo. The majority of ⁹⁹Mo heretofore producedfor ^(99m)Tc medical use comes from fission in nuclear reactors, andmust be processed carefully to remove nuclear contaminates.

20 million diagnostic nuclear medical procedures every year use^(99m)Tc, approximately 85% of diagnostic imaging procedures in nuclearmedicine use this isotope. Depending on the type of nuclear medicineprocedure, the ^(99m)Tc is bound to different pharmaceutical thattransports it to the required location. ^(99m)Tc is chemically bound toSestamibi when it is used to image the blood flow, or lack thereof, inthe heart. Since Exametazime, is able to cross the blood brain barrier,^(99m)Tc is used with Exametazime so the ^(99m)Tc flows through thevessels in the brain to image cerebral blood flow. Imaging of renalfunction is accomplished by tagging ^(99m)Tc to Mercapto Acetyl TriGlycine.

Similarly, ¹¹¹In is a radionuclide with a half-life of 2.8049 days andwith gamma ray emissions of 171.2 and 245.3 keV. In a chloride form, itis used as a bone marrow and tumor-localizing tracer; in a chelate form,as a cerebrospinal fluid tracer and in a trichloride form, is used inelectron microscopy to stain nucleic acids in thin tissue sections. Itdecays by electron capture:

¹¹¹In→¹¹¹Cd+γ(171.2 keV)+γ(245.3 keV)

Electron capture decay can be though of as a positron decay where thepositron is destroyed in the nucleus by an captured electron. In thiscase the decay produces the gamma ray emissions of 171.2 and 245.3 keVsensed in the PET scan.

For many applications, due to short half-life and/or low productionyield, it is necessary to use an intense alpha particle beam in order toproduce reasonable quantities of ⁹⁹Mo or ¹¹¹In. Particles beams of thetype described herein may be used to produce diagnostic ortherapeutically effective doses of these materials. As used herein, thephrase diagnostic or therapeutically effective dose is to be understoodto mean a dose sufficient to perform at least one diagnostic ortherapeutic procedure is a human or animal patient.

Advantageously, the devices and techniques described herein may be usedto produce usable quantities of ⁹⁹Mo or ¹¹¹In without the use a nuclearfission reactor. Accordingly, production of dangerous radioactivebyproducts may be reduced or eliminated. Also, by using beam targets ofvery high purity, few undesirable products are made so post processingfor isotope purity is improved.

Referring to FIGS. 17A, 17B, and 17C one exemplary production process isto form a target 301 by placing a layer 190 of ⁹⁶Zr atoms on a copperstrip 192 and then place a thin layer 194 of ¹⁰⁹Ag atoms on the layer190 of ⁹⁶Zr atoms. The strip 192 is shown extending between a supplyroll 196 and a take-up roll 198.

A beam from ion source 300 is accelerated by accelerator 310 to target301. In some embodiments, accelerators 310 functions in a pulse mode soafter the beam is spread into a rectangular shape by the beam spreader320, either a pulse or more of alpha particles is directed at arectangular area 330 of the strip 192 (in other embodiments, other beamshapes may be used). The target strip 301 is then indexed or movedcontinuously with respect to the beam. A cooling system can be used tocool the target 301. For example coolant may be circulated via ports350. Any suitable cooling technique known in the art may be used.

In some embodiments, alpha particles are accelerated to the target 301at an energy of approximately 28 MeV to transmute a portion of the ¹⁰⁹Agatoms of layer 194 into ¹¹¹In. Alpha particles passing through layer 194will lose some energy in the process, and thereafter, a portion willimpinge on layer 190 at an energy of approximately 16 MeV, transmuting aportion of the ⁹⁶Zr atoms or layer 190 into ⁹⁹Mo. The copper, ¹⁰⁹Ag,¹¹¹In, ⁹⁶Zr, and ⁹⁹Mo are easy to separate chemically so the copper,¹⁰⁹Ag and ⁹⁶Zr remaining are recycled, and the ⁹⁹Mo and ¹¹¹In arechemically separated and used for medical isotope purposes.

Similar techniques may be used for targets with more that two layers ofdifferent target materials, or with a single layer of target material.

Although embodiments are shown above with target 301 mounted on a roll,and other suitable target mount may be used. In some embodiments, target301 may mounted on a plate (not shown). The target plate is placed infront of the beam to undergo reactions, after which the plate may bechanged. In some embodiments, a target station would support more thenone plate at a time. This allows a first plate to be exposed to the beamwhile another plate is changed out and a new plate made ready during theexposure of the first plate. This reduces beam down time. Further, usingplates in this manner allows the exposed product, which may have a shorthalf-life, to be taken out quickly.

Note that in various embodiments, the systems and techniques describedherein may also be used to produce beams of singly ionized ions. We canalso use the source for production of singly charged ions. In someembodiments the system may selectively operable in several modescorresponding to different ion types and charge state outputs. In someembodiments, a single ion source may be used. Some embodiments mayfeature multiple ion sources. In some embodiments, multiple beams ofvarious types may be generated from a single source, e.g. using chargeor mass filtering techniques.

While particular embodiments of the present invention have been shownand described, it will be obvious to those skilled in the art thatchanges and modifications may be made without departing from theinvention in its broader aspects and, therefore, the appended claims areto encompass within their scope all such changes and modifications asfall within the spirit and scope of this invention. All patents,published applications and articles mentioned herein are incorporated byreference in their entirety.

1. A method comprising: generating an ion beam, said generatingcomprising the steps of: providing a chamber disposed about alongitudinal axis and containing a gas; producing a magnetic field in aconfinement region within the chamber, wherein the confinement region isdisposed about the axis and extends along the axis from a proximal endto a distal end, and wherein the magnetic field comprises: a firstmagnetic mirror located at the proximal end of the confinement region; asecond magnetic mirror located at the distal end of the confinementregion; a substantially uniform magnetic field disposed about anddirected substantially parallel to the longitudinal axis, thesubstantially uniform magnetic field being located between the first andsecond magnetic mirrors; producing a time varying electric field todrive the cyclotron motion of electrons located within the confinementregion; causing said driven electrons interacting with the gas to form aconfined plasma; and confining the plasma in the confinement region suchthat a portion of atoms in the plasma experience multiple ionizinginteractions with the driven electrons to form multiply ionized ionshaving a selected final ionization state; directing the ion beam to atarget comprising a target material; and transmuting at least a portionof the target material to a radio-isotope by a nuclear reaction betweenions in the selected final ion state and atoms of the target material.2. The method of claim 1, wherein the time varying electric field has afrequency substantially tuned to the electron cyclotron resonancefrequency corresponding to the substantially uniform magnetic field. 3.The method of claim 2, wherein the electron cyclotron resonance driverdrives the cyclotron motion of electrons located throughout a volumesurrounding the substantially uniform magnetic field.
 4. The method ofclaim 1, wherein directing the ion beam comprises accelerating the ionbeam.
 5. The method of claim 1, wherein the ion beam has a current of 1mA or greater.
 6. The method of claim 1, wherein the ion beam has acurrent of 10 mA or greater.
 7. The method of claim 1, wherein the ionbeam has a current of 20 mA or greater.
 8. The method of claim 1,wherein the ion beam has a current of 50 mA or greater.
 9. The method ofclaim 7, wherein at least 70% of the ions in the selected finalionization state.
 10. The method of claim 7, wherein at least 80% of theions in the beam are in the selected final ionization state.
 11. Themethod of claim 7, wherein at least 90% of the ions in the beam are inthe selected final ionization state.
 12. The method of claim 1, whereinthe atoms of the target material have a longer half life than theradio-isotope.
 13. The method of claim 1, wherein the ions in theselected final ion state comprise alpha particles or ³He⁺⁺ ions.
 14. Themethod of claim 10, wherein the nuclear reaction between ions in theselected final ion state and atoms of the target material comprise atleast one from the list consisting of: ⁹⁶Zr(α,n)⁹⁹Mo, ²⁰⁹Bi(α,2n)²¹¹At,¹⁴⁴Sm(α,γ)¹⁴⁸Gd, ¹⁴⁷Sm(α,3n), ¹⁴⁸Gd, ¹¹⁴Cd(α,n)^(117m)Sn, and¹¹⁶Cd(α,3n)^(117m)Sn.
 15. The method of claim 1, wherein theradio-isotope comprises ⁹⁹Mo, said method further comprising: generatinga diagnostic or therapeutic effective dose of ^(99m)Tc from the ⁹⁹Mo bynegative beta decay.
 16. The method of claim 15, wherein the entirediagnostic or therapeutic effective dose of 99m Tc is generated withoutthe use of a nuclear fission reactor.
 17. The method of claim 1, whereinthe radio-isotope comprises ¹¹¹In, said method further comprising:generating a diagnostic or therapeutic effective dose of ¹¹¹In.
 18. Themethod of claim 17, wherein the entire diagnostic or therapeuticeffective dose of ¹¹¹In is generated without the use of a nuclearfission reactor.
 19. The method of claim 7, wherein the radio-isotopecomprises at least one selected from the list consisting of: ¹⁸F, ¹²³Xe,¹²³I, ⁶⁷Ga, ¹¹¹In, ¹³¹Ba, ⁶⁸Ge, ⁸²Sr, ⁸²Rb, ⁸⁹Sr, ¹⁵³Sm, ¹²⁴I, ²¹¹At,¹⁴⁸Gd, ⁷⁶Br, ¹⁹⁹Tl, ¹⁰⁰Pd, ¹²⁸Ba, ^(117m)Sn and ²²⁹Th.
 20. The method ofclaim 1, wherein the nuclear reaction comprises fission of atoms in thetarget material stimulated by bombardment with the ions in the selectedfinal state.
 21. The method of claim 1, wherein the target comprises alayer of a first target material overlaying a second target material,the method further comprising: directing the ion beam at a first energyto the layer of first target material such that: a first portion of theions in the beam transmute a portion of the first target material into afirst radio-isotope by a first nuclear reaction between the firstportion of ions and atoms of the first target material; a second portionof the ions in the beam interact with the layer to be decelerated to asecond energy, and the second portion of the ions in the beam transmutea portion of the second target material into a second radio-isotope by asecond nuclear reaction between the second portion of ions and atoms ofthe second target material.
 22. The method of claim 21, wherein the ionsat the first energy more preferentially drive the first nuclear reactionthan the second nuclear reaction, and the ions at the second energy morepreferentially drive the second nuclear reaction than the first nuclearreaction.
 23. The method of claim 22, wherein: the first target materialcomprises ¹⁰⁹Ag, the second target material comprises ⁹⁶Zr, the firstnuclear reaction comprises ¹⁰⁹Ag(α,2n)¹¹¹In, the second nuclear reactioncomprises ⁹⁶Zr(α,n)⁹⁹Mo, the first energy is about 28 MeV, and thesecond energy is about 14 MeV.
 24. An isotope generation apparatuscomprising: an ion beam source which generates an ion beam, the sourcecomprising: a chamber disposed about a longitudinal axis and containinga gas; a magnetic confinement system configured to produce a magneticfield in a confinement region within the chamber, wherein theconfinement region is disposed about the axis and extends along the axisfrom a proximal end to a distal end, and wherein the magnetic fieldcomprises: a first magnetic mirror located at the proximal end of theconfinement region; a second magnetic mirror located at the distal endof the confinement region; a substantially uniform magnetic fielddisposed about and directed substantially parallel to the longitudinalaxis, the substantially uniform magnetic field being located between thefirst and second magnetic mirrors; and an electron cyclotron resonancedriver which produces a time varying electric field which drives thecyclotron motion of electrons located within the confinement region,said driven electrons interacting with the gas to form a confinedplasma, wherein: during operation, the magnetic confinement systemconfines the plasma in the confinement region such that a portion ofatoms in the plasma experience multiple ionizing interactions with thedriven electrons to form multiply ionized ions having a selected finalionization state an extractor for extracting the ion beam from theconfinement region, wherein the beam comprises a portion of the multiplyionized ions in the selected final ionization state; a target comprisinga target material; and an accelerator for accelerating the ion beam anddirecting the ion beam to the target; wherein the ion beam directed tothe target transmutes at least a portion of the target material to aradio-isotope in response to a nuclear reaction between ions in theselected final ion state and atoms of the target material.
 25. Theapparatus of claim 24, wherein the ion beam has a current of 1 mA orgreater.
 26. The apparatus of claim 24, wherein the ion beam has acurrent of 10 mA or greater.
 27. The apparatus of claim 24, wherein theion beam has a current of 20 mA or greater.
 28. The apparatus of claim24, wherein the ion beam has a current of 50 mA or greater.
 29. Theapparatus of claim 27, wherein at 60% of the ions in the beam are in theselected final ionization state.
 30. The ion source of claim 27, whereinat least 80% of the ions in the beam are in the selected finalionization state.
 31. The apparatus of claim 24, wherein the atoms ofthe target material have a longer half life than the radio-isotope. 32.The apparatus of claim 24, wherein the ions in the selected final ionstate comprise alpha particles or ³He⁺⁺ ions.
 33. The apparatus of claim32, wherein the nuclear reaction between ions in the selected final ionstate and atoms of the target material comprise at least one from thelist consisting of: ⁹⁶Zr(α,n)⁹⁹Mo, ²⁰⁹Bi(α,2n)²¹¹At, ¹⁴⁴Sm(α,γ)¹⁴⁸Gd,¹⁴⁷Sm(α,3n)¹⁴⁸Gd, ¹¹⁴Cd(α,n)^(117m)Sn, and ¹¹⁶Cd(α,3n)^(117m)Sn.
 34. Theapparatus of claim 32, wherein the radio-isotope comprises at least oneselected from the list consisting of: ¹⁸F, ¹²³Xe, ¹²³I, ⁶⁷Ga, ¹¹¹In,¹³¹Ba, ⁶⁸Ge, ⁸²Sr, ⁸²Rb, ⁸⁹Sr, ¹⁵³Sm, ¹²⁴I, ²¹¹At, ¹⁴⁸Gd, ⁷⁶Br, ¹⁹⁹Tl,¹⁰⁰Pd, ¹²⁸Ba, ^(117m)Sn, and ²²⁹Th.
 35. The apparatus of claim 24,wherein: the electron cyclotron resonance driver produces a time varyingelectric field having a frequency substantially tuned to the electroncyclotron resonance frequency corresponding to the substantially uniformmagnetic field; and the electron cyclotron resonance driver drives thecyclotron motion of electrons located throughout a volume containing thesubstantially uniform magnetic field.
 36. The apparatus of claim 24,wherein the magnitude of the substantially uniform magnetic field variesby less than 10% over a region disposed about the longitudinal axis,said region located midway between the first and second magnetic mirrorsand extending along the longitudinal axis over a distance equal to atleast about 25% of the axial distance between the first and secondmagnetic mirrors.
 37. The apparatus of claim 24, wherein the magnitudeof the substantially uniform magnetic field varies by less than 5% overa region extending at least 15 cm along the longitudinal axis.
 38. Theapparatus of claim 24, wherein the magnetic field is azimuthallysymmetric about the longitudinal axis throughout the confinement region.39. The apparatus of claim 24, wherein the target comprises a layer of afirst target material overlaying a second target material.
 40. Theapparatus of claim 39, wherein the accelerator directs the ion beam at afirst energy to the layer of first target material such that: a firstportion of the ions in the beam transmute a portion of the first targetmaterial into a first radio-isotope by a first nuclear reaction betweenthe first portion of ions and atoms of the first target material; asecond portion of the ions in the beam interact with the layer to bedecelerated to a second energy, and the second portion of the ions inthe beam transmute a portion of the second target material into a secondradio-isotope by a second nuclear reaction between the second portion ofions and atoms of the second target material; wherein the ions at thefirst energy more preferentially drive the first nuclear reaction thanthe second nuclear reaction, and the ions at the second energy morepreferentially drive the second nuclear reaction than the first nuclearreaction.